Author Topic: Ran great last week - come back this week and... not so much  (Read 8558 times)

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Offline ev0lve

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Ran great last week - come back this week and... not so much
« on: April 12, 2009, 08:55:53 PM »
Hi there,

I've got a machine I thought I was close to riding away but maybe not. Last week I gave it a tune up and I thought it was running great. It's always been hard starting since I buttoned up the engine but I thought syncing the carbs would help that. Maybe not.

Here's what I did to it last week
http://forums.sohc4.net/index.php?topic=38242.msg520008#msg520008

This week it's been sitting for a week. No one's touched it. Still very hard to get started.

It's got the plugs in it that have been in there since November last year when I buttoned up the motor.

The air screws are 1 turn out, vacuum synced and it ran great (I thought) last week.

The battery had been on a tender all week long.

Spin the starter motor for a few minutes and it gurgles, catches a little, gurgles catches a little. Doesn't seem to matter with the choke on or off.

Finally catches and I run it for awhile. Sounds like it's running on 3 cylinders. Let it warm up. More of the same. Bogs when giving it throttle (bogs maybe a little strong - not as responsive as last week). Pipes are all hot. #1 is hot enough that it's smoking a bit. Didn't do that last week either. Here's a video once it warmed up

Edit: Ha. I didn't even realize I let out that heavy sigh till I just watched it  :D

I'm just at a loss as to what could have changed from last week to this other than the spark plugs condition. I have a new set to install next time I get up there but I need a little help formulating a systematic game plan.

I'd really like to get this machine out of the garage this week. Let me know if there's any info I left out that would ring bells and thanks!
« Last Edit: April 12, 2009, 09:26:51 PM by Iggy »

Offline 750goes

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Re: Ran great last week - come back this week and... not so much
« Reply #1 on: April 12, 2009, 09:54:35 PM »
If you have response problems and it does not want to idle very well?

First off I would check the idle jets, then the mains, then the emulsion tubes, and the idle circuits - in other words give the carbs a full 100% clean up -

I would maybe even pick up the idle a bit..

Before you synched the carbs what other work have you done to it ?


Offline Hush

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Re: Ran great last week - come back this week and... not so much
« Reply #2 on: April 12, 2009, 09:58:06 PM »
I'd turn air screws in about a 1/4 each, I don't know much about the 750 but sounds like she is getting too much air at start-up.
What do the plugs look like when removed?
Best indicator to engine condition you can get is plugs, I'm betting they wont be black and fluffy, probably very white.
How much gas in the tank? how old is it? is tank filter clean?
But I'm only making some guesses here and filling in till a real 750 buff comes along. ;D

Oh yeah and tell that flaming monkey to quit smoking!!! >:(
« Last Edit: April 12, 2009, 10:04:50 PM by Hush »
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline martino1972

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Re: Ran great last week - come back this week and... not so much
« Reply #3 on: April 12, 2009, 10:31:56 PM »
I know what's wrong...your shifter fell off....... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D

um....does your timing advance work freely...???
Marti, I want you to know, I like you an awful lot, but guys have said far less and left wearing their drinks on their shirts.
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Offline TwoTired

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Re: Ran great last week - come back this week and... not so much
« Reply #4 on: April 13, 2009, 01:32:19 AM »
You're going to feel silly adjusting on carbs if you have a fouled spark plug.
Look at the tips of them.  They are your window to the combustion condition inside the chambers.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Is that a big loop of fuel line from tank to carbs?  It's supposed to be gravity feed.  Which means a constant drop in the feed pipe from source to destination. (tank to carb nipples)  There is very little force making the fuel climb up the pipe.  And any air in the line will try to fight the flow.

Did you check to see if all carbs have fuel in the bowls?

The carbs have mechanical slides.  The position of the slides determines which part of them are feeding the fuel.  Idle/pilot system is dominant up to 1/4 throttle, the throttle valve from 1/4 to 3/4, the main 3/4 to WOT.

If, for example, you have a single idle jet plugged or starved from fuel, opening the throttle to midrange will supply fuel sans what small contribution the pilot system provides; lean/hot is the result for that cylinder.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
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Offline andy750

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Re: Ran great last week - come back this week and... not so much
« Reply #5 on: April 13, 2009, 04:17:21 AM »
+1 on the giant loop of fuel line - first thing I noticed! It does sound like you are starved for fuel or running on 3 so easiest thing to do first is to change the plugs then do as TT recommends and check fuel is getting to the bowls - again easy enough to check. Id also check spark at each plugs - done by holding the plug against the cylinder head - may be you have a poor connection between HT wire and plug -trim ends to rectify this if thats the case. Lastly Id adjust that camchain - sounds like a tractor!

Good luck!
Andy

Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
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Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #6 on: April 13, 2009, 08:03:31 AM »
If you have response problems and it does not want to idle very well?

First off I would check the idle jets, then the mains, then the emulsion tubes, and the idle circuits - in other words give the carbs a full 100% clean up -

I would maybe even pick up the idle a bit..

Before you synched the carbs what other work have you done to it ?


One of the first things was a full rebuild and cleaning of the carbs back in September along with a top end rebuild. It sprang straight to life on the first go at 5000 RPM. I took them back off and bench synced them properly which turned out well and it idled at about 1200. So I think the carbs work.

Did the tune up last week. Didn't replace the points. Timed it. Lubed the points cam. Ran very very well I thought. Tight response up to redline and back down smoothly.

I'd turn air screws in about a 1/4 each, I don't know much about the 750 but sounds like she is getting too much air at start-up.

That occurred to me and will do. They had been turned all the way in.

Quote
What do the plugs look like when removed?
Best indicator to engine condition you can get is plugs, I'm betting they wont be black and fluffy, probably very white.
Don't know yet. I stole a couple hours of Easter family time to mess with the machine.
Quote
How much gas in the tank? how old is it? is tank filter clean?
But I'm only making some guesses here and filling in till a real 750 buff comes along. ;D
Not sure. Half a tank maybe. Less than a month old. In tank filter looked pretty good. Swapped it out from my old tank.
Quote
Oh yeah and tell that flaming monkey to quit smoking!!! >:(

The monkey is stubborn but if I can get it out of the garage that's the plan  ;D

I know what's wrong...your shifter fell off....... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D

um....does your timing advance work freely...???
;D You can see the dowel for the centerstand in the background there too. Yes, it seems to work fine.

Sorry for not getting back last night but the forum was giving me timeouts.


Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #7 on: April 13, 2009, 08:11:39 AM »
You're going to feel silly adjusting on carbs if you have a fouled spark plug.
Look at the tips of them.  They are your window to the combustion condition inside the chambers.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

That'll be the first thing I think, replacing the plugs and seeing what they think is going on.

Quote
Is that a big loop of fuel line from tank to carbs?  It's supposed to be gravity feed.  Which means a constant drop in the feed pipe from source to destination. (tank to carb nipples)  There is very little force making the fuel climb up the pipe.  And any air in the line will try to fight the flow.

I was wondering about that. I had the tank up on a stand while tuning it so there was 8 - 12 inches more room for the gas to fall through.

Quote
Did you check to see if all carbs have fuel in the bowls?
Nope. Most of the family was around for Easter so it was pretty quick. Just trying to get a checklist together for when I can spend a day with it.

Quote
The carbs have mechanical slides.  The position of the slides determines which part of them are feeding the fuel.  Idle/pilot system is dominant up to 1/4 throttle, the throttle valve from 1/4 to 3/4, the main 3/4 to WOT.

If, for example, you have a single idle jet plugged or starved from fuel, opening the throttle to midrange will supply fuel sans what small contribution the pilot system provides; lean/hot is the result for that cylinder.

Cheers,



Given that #1 was smoking a bit and not at all last week I think the lean condition makes sense (as much as I've accumulated info as to why things do what they do anyways)

Petcock has been off. Can they glaze up that fast? I suppose there's a fair amount of gas in the long line?

Thanks!

Offline my78k

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Re: Ran great last week - come back this week and... not so much
« Reply #8 on: April 13, 2009, 08:14:25 AM »
Were the carbs stored empty or full since last Sept? Also, if there was any sediment in the float bowls last week it could have easily been sucked into one of the idle jets this week. Condition of the tank? Fuel filter?

Dennis

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #9 on: April 13, 2009, 08:14:54 AM »
+1 on the giant loop of fuel line - first thing I noticed! It does sound like you are starved for fuel or running on 3 so easiest thing to do first is to change the plugs then do as TT recommends and check fuel is getting to the bowls - again easy enough to check. Id also check spark at each plugs - done by holding the plug against the cylinder head - may be you have a poor connection between HT wire and plug -trim ends to rectify this if thats the case. Lastly Id adjust that camchain - sounds like a tractor!

Good luck!
Andy


;D Thought I did adjust the cam chain. Well, won't hurt to do it again. Have ended up doing most everything twice so far.

Can do on the checklist and cleaning up the plug wires.

Thanks to all you guys for the responses! I'll post back in a couple days when I get up there to work on it!

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #10 on: April 13, 2009, 08:32:45 AM »
Were the carbs stored empty or full since last Sept? Also, if there was any sediment in the float bowls last week it could have easily been sucked into one of the idle jets this week. Condition of the tank? Fuel filter?

Dennis

Mostly empty - hasn't had a tank with gas on it until a couple weeks ago. The tank itself has some sediment in it for sure but I tried to get it all out when I got it.

"Shouldn't" be much in the bowls given the amount of use they've gotten (been started and run maybe 4 times since March).

The inline filter is mostly there to be a joint between the long piece of hose and the short attached to carbs so I could plop the tank on a makeshift stand for tuning. Here's a pic of the petcock that came out of the tank (leaky) and the one I replaced it with from my old tank.


« Last Edit: April 13, 2009, 08:56:33 AM by Iggy »

Offline goon 1492

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Re: Ran great last week - come back this week and... not so much
« Reply #11 on: April 13, 2009, 09:46:40 AM »
Man I'd say something to help but it looks like everyone else said it all, even the fuel line, that will give you endless trouble. Could even be part of the funny cam chain sound if one cyclinder is getting just enough fuel to fire on.
Last year I tried running an inline filter, kept getting a lean running condition after a few minutes of idling, shut it off and the bowls' would have time to trickle and refill and it would run like a top again upon next startup and then chuga chug chuga chug.. Never could get that air bubble out.
I listened to TT took it off and never doubted him again.

Oh I have some original tank logos and a brake and clutch lever coming your way!
The brake and clutch lever is off of a 74, I cut the ball ends off of them and polished them too. I noticed on my 76 that the clutch lever is the same as 74 but the brake lever is different than mine, not sure if the brake lever would do you any good since you are using a different MC but spare parts are good for horse trading at swap meets and such so...
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Offline gregk

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Re: Ran great last week - come back this week and... not so much
« Reply #12 on: April 13, 2009, 09:55:50 AM »
Regarding the static pressure in the fuel line, if you have say 10" of fall from a full tank to the petcock, you will only have about 0.3 psi at the tap. Not really a lot of pressure!  if the fuel line was open to the atmosphere, the fuel level would be approximately that of the tank.  I have seen this used to check float levels in carbs where a line is attached to the bottom of the carb bowl and looped upward along the bowl and the static level is then the level of gas in the bowl. 

Greg
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Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #13 on: April 13, 2009, 09:59:20 AM »
Man I'd say something to help but it looks like everyone else said it all, even the fuel line, that will give you endless trouble. Could even be part of the funny cam chain sound if one cyclinder is getting just enough fuel to fire on.
Last year I tried running an inline filter, kept getting a lean running condition after a few minutes of idling, shut it off and the bowls' would have time to trickle and refill and it would run like a top again upon next startup and then chuga chug chuga chug.. Never could get that air bubble out.
I listened to TT took it off and never doubted him again.

Oh I have some original tank logos and a brake and clutch lever coming your way!
The brake and clutch lever is off of a 74, I cut the ball ends off of them and polished them too. I noticed on my 76 that the clutch lever is the same as 74 but the brake lever is different than mine, not sure if the brake lever would do you any good since you are using a different MC but spare parts are good for horse trading at swap meets and such so...

You know, the only thing that's different here is the tank was on the stand when I tuned it up last week. The fuel line is some I got from Schuck's and it's tight. The ID is definitely less than stock. Tight enough I'll have to cut it off the spigots.

I suppose a positive test for dumb-assery is to fill the tank and put it up high again first thing and see if it runs fine. If it does I guess I'll be replacing the fuel line with the right ID.

Edit: The right ID is 5.5mm



And man, you didn't have to do that. THANKS!  ;D ;D ;D ;D ;D ;D ;D ;D ;D
« Last Edit: April 14, 2009, 03:47:57 PM by Iggy »

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #14 on: April 13, 2009, 10:10:03 AM »
Regarding the static pressure in the fuel line, if you have say 10" of fall from a full tank to the petcock, you will only have about 0.3 psi at the tap. Not really a lot of pressure!  if the fuel line was open to the atmosphere, the fuel level would be approximately that of the tank.  I have seen this used to check float levels in carbs where a line is attached to the bottom of the carb bowl and looped upward along the bowl and the static level is then the level of gas in the bowl. 

Greg

I'm wondering that something like that isn't the issue here re: smaller id fuel line.

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #15 on: April 13, 2009, 10:54:37 AM »
BTW, I'm working on this thing all by my lonesome in my Pop's garage as time permits so wanted to give a large THANK YOU to everyone here on the forum.

Kind of like having buddies that drop by to give advice but don't drink all your beer  ;D

Thanks again!

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #16 on: April 18, 2009, 12:57:28 AM »
Well, here's what the plugs I replaced looked like. Not unexpected I guess as I hadn't tuned anything up prior to the last go around.



Then I gapped up the new set, clipped the wires and redid the caps getting ready to do a plug chop and see if there's anything I can see. Tanks back up on the stand and, since I couldn't find any 5.5mm fuel line this batch is 6.3mm. I think it solved the issue of leaning out but I'll get to that.

Would you take a look here and let me know if there's anything I can do about getting it started. The choke doesn't seem to do much on or off until it's started. I know it's working as I've seen the slides close. The abuse at the end is the chop. I think I'm doing it right but let me know if I'm missing some nuance  ;D

The PO had the clips set down one notch (second from the bottom) and it would start lickety split. I moved them back to the middle position and that's when it started not wanting to start.

Anyways, the chop looks like this



Which is better I think but I don't know how indicative it is of the long term.

Finally I took the tank off the stand and put it back on the bike. Cut the 6.3 to length and found I didn't really want to run it in front of the choke. So I did this...


Seems to run pretty well in this configuration. I don't see it being a problem but that doesn't mean it isn't. Please let me know if you guys do.

Lastly, I removed most of the tractor from it bringing the idle up to around 1100 instead of below a 1000 (the garage plays up the rattling a bit). There's this kind of ururururururur action going on when holding the throttle at 5000 or +

What is that? Timing or more carb work? Why?

Thanks again! I really appreciate it!


Offline 750goes

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Re: Ran great last week - come back this week and... not so much
« Reply #17 on: April 18, 2009, 01:06:18 AM »
Sounds good, does the rattle go away a bit when you pull the clutch in ??


Offline Hush

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Re: Ran great last week - come back this week and... not so much
« Reply #18 on: April 18, 2009, 01:08:53 AM »
The bottom film sounds at the begining like your carbs are out of sync?
Maybe the PO had the needles set like that to accomodate the non stock exhaust, going 4 into 1 means a lot of carb fiddling.
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline martino1972

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Re: Ran great last week - come back this week and... not so much
« Reply #19 on: April 18, 2009, 01:12:33 AM »
don't know man....almost doubt it's fuel related.......bad resistor cap,points out of time or advange not working as should....
the reason i think it's electrical cause it started doing it at once...not slowly getting worse over time....other wise i would say,worn needles etc......
Marti, I want you to know, I like you an awful lot, but guys have said far less and left wearing their drinks on their shirts.
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Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #20 on: April 18, 2009, 01:24:07 AM »
Sounds good, does the rattle go away a bit when you pull the clutch in ??



Not sure. I think the garage amplifies the rattle a bit. I took a vid of it's first voyage outside the garage and it sounds MUCH better outside than in.


The bottom film sounds at the begining like your carbs are out of sync?
Maybe the PO had the needles set like that to accomodate the non stock exhaust, going 4 into 1 means a lot of carb fiddling.

The Kerker is new with me. Had a 4 - 2 previously (you can see it against the back wall there). There was a nice hole in #2 someone poked in it with a screwdriver it looks like. I JB Welded it up so I think the PO may have had even less experience than me.

Just synced them a couple weeks ago after tuning it.



Probably ought to go over it again. I did put the timing light to it today and both sets show up on the F (with some flutter) and in between the marks on advance.

don't know man....almost doubt it's fuel related.......bad resistor cap,points out of time or advange not working as should....
the reason i think it's electrical cause it started doing it at once...not slowly getting worse over time....other wise i would say,worn needles etc......

Doh. Tell me more about the at once vs over time? You mean this instance - that RPM? I feel like the bog I described in the first post was solved with the fuel line replacement BUT there's still 4.8mm in between as the connectors.

What is that sound


Offline martino1972

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Re: Ran great last week - come back this week and... not so much
« Reply #21 on: April 18, 2009, 03:14:30 AM »
um......some problems with bikes start over time,meaning   it slowly get's worse to the point of where you starting to get enoyed by it....or,instant change in behavior......yesterday it ran perfect,today it run's weird.......
things wearing out,getting slowly out of sync will be over time.........an component failing will be like....hey,she didn't do this yesterday kinda thing......

mechanical things wearing out would be mostly "things happening over time" ,unless it happens with a bang,something breaks and stops functioning...like a engine seasing up,a connecting rod breaking.....

electrical things are mostly under the "hey,she didn't do this yesterday" kinda thing......

hope i'm making any sense here.... :D
Marti, I want you to know, I like you an awful lot, but guys have said far less and left wearing their drinks on their shirts.
http://forums.sohc4.net/index.php?topic=36933.0  (my bobber)

Offline Hush

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Re: Ran great last week - come back this week and... not so much
« Reply #22 on: April 18, 2009, 04:49:44 AM »
When you changed from the 4 into 2's to the Kerker (which I presume is a 4 into 1) did you rejet the carbs?
Just wondering as this seems to be quite an important point when altering the exhaust systems on these SOHC 4's.
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline ev0lve

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Re: Ran great last week - come back this week and... not so much
« Reply #23 on: April 18, 2009, 09:51:00 AM »
um......some problems with bikes start over time,meaning   it slowly get's worse to the point of where you starting to get enoyed by it....or,instant change in behavior......yesterday it ran perfect,today it run's weird.......
things wearing out,getting slowly out of sync will be over time.........an component failing will be like....hey,she didn't do this yesterday kinda thing......

mechanical things wearing out would be mostly "things happening over time" ,unless it happens with a bang,something breaks and stops functioning...like a engine seasing up,a connecting rod breaking.....

electrical things are mostly under the "hey,she didn't do this yesterday" kinda thing......

hope i'm making any sense here.... :D

Well, I do have some electrical issues I have to work out but they don't seem to be affecting the ignition part of the show - so far. I'm sure I can fiddle the bucket into non-running status given a chance though  ;D The start issue is pretty much right after the carb/top end rebuild. Once it's warm it's right in the pocket to start up.

I suspect the small diameter hose connecting the carbs. In that video it starts up kind of slowly like it finally drew enough gas (total guess). But based on the way it starts in the video does that make sense?

When you changed from the 4 into 2's to the Kerker (which I presume is a 4 into 1) did you rejet the carbs?
Just wondering as this seems to be quite an important point when altering the exhaust systems on these SOHC 4's.

Nope, stock rebuild kits (110's if memory servers - K&L kits). What does the urururururur sound holding the throttle open suggest do you think?

Offline TwoTired

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Re: Ran great last week - come back this week and... not so much
« Reply #24 on: April 18, 2009, 12:15:14 PM »
Some observations:  And note I'm trying to be objective, not harsh, simply to get the point across quickly.

In the video, you prolonged the start up process by removing the choke.  If it's cold, leave it on for start up.  You don't have an accelerator pump to add extra fuel during cold start. But, the choke plates (not slides) closed at the carb entrance, increase the throat vacuum applied to all the jets.  The throttle valve and main are mostly closed when the throttle is placed in the idle position.  If you want more fuel during cold start, whack the throttle open while cranking with the choke closed, so the throttle valve can supply fuel as well.

D8 plugs don't run well cold, particularly at idle, as they are designed to wick away heat from the chamber.  Don't expect it to start and run at idle when cold.  Use the 2000 or 3000 RPM throttle position when it's cold for starting.  Many other machines change the idle position upward when choke is applied.  Honda felt that 750 owners were smart enough to operate the throttle manually when the engine was cold.

Those blacken plugs show conductive soot between the center electrode and the plug body.  Soot is conductive.  Why would electricity leap the difficult spark gap, when it could just meander the soot trail?

Plug chops need to be done when the engine is making power.  Not much power is made by the engine when the bike is on the center stand and the rear wheel free wheeling. 
Further, your complaint was idle, and you revved the engine so as to operate on a completely different jet supply than idle and the engine combustion was at far higher temps then at idle.  Doesn't this seem a bit unreasonable to diagnose an idle mixture or start up issue?

Finding neutral with the clutch in will be easier if you make the rear wheel move (either direction).

Although, it is worth while to check the plug cap resistance, it doesn't sound (when running) like there is a specific ignition issue at all.

During electrical start up, the starting motor puts a big draw on the battery.  While supplying these large currents, the battery voltage dips.  As the coils rely on source voltage to make spark voltage, a dip in supply means a dip in capability.  Cold engines are harder to turn over than hot ones, leading to higher current draw from the starter motor.
If the bike's electrical connectors, switches, etc. in the path between battery and coils is also losing voltage, the starter dip plus those losses might make the spark marginal during electric start.  And, this would be worsened if the headlight is on as well, adding it's current draw.  To determine if this is part of your start up issue.  Use a voltmeter to check the voltage getting to the coils during start up.  If below 9V, then suspect a spark problem at startup.

Finally, quick starts were alway indicative of recent tune up completion.  Valve settings, timing, dwell, air filter, cam chain adjust, and new spark plug all made the bike (when new) start quickly.  They still ran crappy when cold, and D8 plugs extended the "crappy" period duration.  Extra RPM would compensate for this somewhat.  But, if the engine is cold, don't try to start it with the controls set where it is known to run crappy.

Hope this helps,







Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.