Topic: Hesitation on Acceleration plus Excessive Backfire on Deacceleration

[YoungBlood]

#3 (edit) after plug chop

[YoungBlood]

Number two

[YoungBlood]

Number four

[YoungBlood]

Number one. I’m going to review that excellent link on NGK plugs. Also will attach a video of the idling today after readjusting timing, and greasing pivot points of advancer mechanism.

[Alan F.]

Two of those plugs look great, 1 lean and 1 rich, if I'm not mistaken.

There was a thread a while back where a member took a bunch of genuine Keihin jets and some aftermarket jets to work and measured them with a highly acurate scientific imaging/measuring device in an effort to determine how close the aftermarket jets were to the stock jets of the same size. I guess stock genuine Keihin were quite consistent but the aftermarket were all over the chart ranging from close to stock to one number higher or lower. Which would explain why your plugs range from lean to nice to rich.

I'd bet the stock jets will be more consistent across all 4 cylinders.

The stock needles may have a different taper, width or length than the stockers also.

And lastly the float needles, I've heard things that the ones that come in some kits are a different length from the stockers, so measuring float height with a gauge may not show you actual fuel level in comparison to the "clear tube method"

Seems like you're making good progress and learning a lot of 'what and why' along the way. Cheers for you there!

If you check ebay for Tec points, be sure to set advanced search to look at eBay stores, sometimes items in ebay stores don't come up in regular searches and just wind up sitting unsold. Cb750A, CB750K, CB750F, and CB750 SOHC are good search terms to find points plates.

Good luck.

[YoungBlood]

Video 1, where I greased the advance mechanism, and how it is now operating. Unsure whether this is good enough, or whether it seems off? https://drive.google.com/file/d/1qOR0Clnujjct3fMIpjTkAvMySC1xP84J/view?usp=sharing
Video 2, Bike running in neutral after setting timing and greasing advance pivots: https://drive.google.com/file/d/1Zzrr7ZN0wddoHTiXRB6FzLbN8W7q140o/view?usp=sharing
Video 3, slack in advance mechanism: https://drive.google.com/file/d/1_mjR0kx2iABgUDfP4p2yZyPZ1GS9yIQM/view?usp=sharing

[YoungBlood]

Alan I think you’re right about the 1 rich 1 lean. And I’m convinced now that I want my old keihin parts back in. I’m going to try to do the main and slow jet for the time being. I’ve got somewhere to be tomorrow. What do you think of electrical ignition, and scrap the points? My sister wants to get me a b-day gift. Is dyna any good? Will I see an improvement, and also save some time and energy? Everyone seems pretty split on the topic, and I’d like to know if any brand is trustworthy.

[Alan F.]

Video 2 won't play. I'll delete this post if you get it working later, no need to reply.

I'm not sure what I'm looking for, can't determine advancer function without a strobe timing light.

Does it ride differently with the advancer lubed up?
Was the advancer less free to move before you lubed it?

There is potential for good results here.

[Alan F.]

Alan I think you’re right about the 1 rich 1 lean. And I’m convinced now that I want my old keihin parts back in. I’m going to try to do the main and slow jet for the time being. I’ve got somewhere to be tomorrow. What do you think of electrical ignition, and scrap the points? My sister wants to get me a b-day gift. Is dyna any good? Will I see an improvement, and also save some time and energy? Everyone seems pretty split on the topic, and I’d like to know if any brand is trustworthy.

The Hondaman Ignition has a lifetime warranty and uses the points still, leaving the points in place as a handy backup in case you need to revert back.

I'd run a search for them, you won't go wrong. Otherwise there are Dyna, which some have had great results with for decades and some have had bad luck with. There are Pamco ignitions with similar win/loss ratios but they're now out of business so no factory support anymore, and Terry from Australia is using a brand that seems to warrant some investigation, I forget the name but search and you'll find or just ask him and he'll tell, best kind he is. I'll probably go with Hondaman's on mine if I ever finish the damn things.

There's a member over on the Honda Twins forum who goes by Ancientdad, his signature reads, " Running points, because I'm tired of mysteries that begin with pushing." A good lesson, if you switch to an electronic ignition, carry your points plate with you, at least for a while....

[YoungBlood]

At the 3:30 mark you should hear the hesitation I've been experiencing. https://drive.google.com/file/d/1_MEhT6v1wfe2IjaWE6vJAIg53X50eNCa/view?usp=sharing I'm not sure about video #2 Alan, it opens when I click the link, and I allowed anyone with the link access. I'll try to re-load it to another google drive folder:   https://drive.google.com/file/d/1VaH4Uwch3V2MA-9zQ18D1fCy0Hl91cXe/view?usp=sharing
The advancer was a bit stiff at one point, some restriction around 1/4 of the weights opening against the springs. The lube helped somewhat, but it was hard to really tell. The restriction was so miniscule at first. After putting it back on, I noticed the play of about an 1/8 inch with the advancer unit when mounted. I also reset the timing, but I can't really notice a difference.
TwoTired's comment about the coil power from the starter housing, and to check all connections and voltage value seems spot on. Scottly a while back told me to check that out, it slipped my mind with all the additional feedback I was receiving.
Strangely enough, the bike seems to have episodes of this hesitation. After I did the recording, I turned the bike off, restarted it and it seemed the hesitation lingered less. Once again, I think this points to TwoTired thinking about the electrical connectors and the vibrational effects on loose connectors.
Thanks for the info Alan, I'll check out the Hondaman Ignition. A friend recently got me the Hondaman manual, I can't wait for it to arrive. Good stuff! If I do switch over, I'll surely keep that plate with me, I'd be a sad camper if I was in the middle of Timbuctoo.

[Jerry Rxman Griffin aka MuthaF'er]

You mentioned changing your jets to aftermarket and then talk about putting the Keihin brass parts. Can you tell us what jets and needles are in the carbs right now and who made them or where they came from?
Aftermarket brass tends to lead to numerous problems trying to tune them. Same is true for several brands of electrical points and condenser parts. The Diachi /Daichi (little propellor logo) are famous for being junk out of the box where condenser is dead or dies quickly and points impossible to properly time.

And what air scrws are you using? Stock ones I HOPE?

[Alan F.]

The slop between the advancer and the crank troubles me, can anyone confirm this is normal or abnormal?
I'm searching but not finding.

Video here:
https://drive.google.com/file/d/1Zzrr7ZN0wddoHTiXRB6FzLbN8W7q140o/view?usp=sharing

[TwoTired]

I listened to your sound recording.  I wouldn't be happy with the bike, either.
Sure wish I could see the plug tips right after that sound recording.  All that sputtering is cylinder misfires.  Which can happen, with fouling plugs.  These motors are known for their smooth running.  Yours never does in that recording.  That it happens during acceleration, too, is not that surprising.

So, I wonder what it sounds like right after installing new, totally clean plug tips.  Still sputter?  Then pursue erratic spark.

If the sputter doesn't happen for a while after new plugs indicating consistent spark, then we're back to an over rich condition fouling plugs and that creates the misfires.

I notice that you seem to ride mostly at low RPM.  Below 4000, unless I miss my guess.   I'm reminded of the movie A New leaf, where the rich guy with a Ferrari in the city was always having it towed to the shop, where they told him every time that the problem was that it had carbon on the valves.  Walter Matthau's oration was quite funny.  Anyway, city driving doesn't let the motor rev and work hard.  That's what burns carbon off the valves and the spark plugs clean in high performance carburetted engines.   BTW, that also makes embers light off mixtures in the exhaust, too.  But, I didn't hear much of that in the recording.  Just a misfiring, stumbling motor, that would drive me nuts.

One of the advantages of having several bikes is being able to swap in known working parts to eliminate what is or is not the problem.

I'll ask if the whole tune up check list has been performed.  Valves adjusted?  Any chance there was a compression check?  It's a comfort to know the engine mechanicals are NOT part of the issue.

Were it here I would swap in an entire points plate assembly with one I KNOW works to eliminate spark issues.  If it doesn't misfire with new plugs, then into the carbs I'd go.

Did you notice any shiny spots on the slide needles?  This would indicate wear on them as well as the needle jet, creating larger orifices.  Quite possibly contributing to different deposit patterns on plugs coresponding the the wear level in each specific carb.  At any rate the spark plug deposit patterns may help in path of scrutiny.  If 1-4 2-3 aligned then spark it where to look.  If across that association, then more likely carb in induction related.

Did you determine where the advancer slop is coming from?  I never noticed that before on my bikes.

Sorry can't help more.

Cheers!

[Alan F.]

Aha!  I think I might have something for you here:
Hondaman's reply #51 replying to Pewe from reply #47

http://forums.sohc4.net/index.php/topic,120687.msg2052482.html#msg2052482

Advancer unit on CB750 must be set in its counterclockwise position of its play before tighten it. F, T and full advance will then match case mark.

If other end position of its play, ignition will be too advanced when matching up with case mark. I have seen this on 2 different cranks.

This happens often after the crankshaft was turned CCW direction with the big nut by the points, with sparkplugs installed. It makes the hole in the end of the crank (which locates the spark advancer peg) oval, and loose. I also have seen cases where the pin on the advancer is smaller than the hole in the crank (!), so then I take a thin, small piece of brass sheet and wrap it around the pin before sliding it back onto the crankshaft. This removes the slop, and often puts the "T" mark on dead-top-center afterward.

And to go along with that:

Reply #107 from Mystic_1
http://forums.sohc4.net/index.php/topic,155076.msg1785749.html#msg1785749

The advancer locknut doesn't hold the points plate, it just secures the advancer to the end of the crankshaft.

I want to say the advancer shaft is smaller than 6mm, probably more like 4mm?  Standard torque on a 6mm fastener is 5 lb-ft, the nut on the advancer is gonna be less than that.

I've never torqued one with a torque wrench.  Slightly more than snug with a 1/4" drive socket will hold it in place.  Use a drop of blue locktite if you want some insurance.

mystic_1

[Alan F.]

Stock exhaust: http://forums.sohc4.net/index.php/topic,187149.0/topicseen.html

[YoungBlood]

Okay, so I think you got something. I believe my slop has caused my static timing to be set off. If you look at that video you can see the amount of slop. Problem is, which slop direction should I tighten the nut for the auto advance mechanism. All the way left, right, or middle? There’s no way for the slop to have the T mark match the index marker, nor the F. The dowel fits into the case port without the T or F lining up on the index. Thus, I don’t see how I find where the perfect spot will be now that the case port for the dowel has expanded in diameter.
Twotired, normally I can get up to 4K rpm range, but I cannot because of how poorly the bike is running. I’m pretty sure something is going on timing wise, I’m going to pick up a strobe gun, but Tec point ears.
I’ll do another plug chop. Put new plugs in on the way home, and take a recording. IM NOT HAPPY TOO. Confused, need to think about other things, but I’ll figure it out.
No, but I put the Keihin slow and main back in. Will put the stock air screw soon.
Has nobody noticed yet that I have to set my timing plate for 1/4 with the two screws on the base off the plate? If I try to use all three screws the timing is too far advanced. Also, over the past three months every time I double check the timing I’ve had to move that plate further clock-wise. Now I can’t even get all three acres in or the timing is off for 1/4. It is a stock TEC plate but non-stock contact breakers. Sorry Twotired, I mean to respond more about what you said, I’m on my cell phone. Gotta get home. Thank you for the advice, I’m pretty sure the needles were worn and shiny, and yeah I didn’t replace the after market needle jet along with the needle, just the needle with the old needle jet. I think that’s something too.

Damnit, damnit, damnit.

[Alan F.]

Just typed for 3 minutes and now my post has vanished, I'm pissed too.


Loosen your advancer nut, turn your advancer counter clockwise to the end of the slop and tighten the nut.

Then test ride it and tell us how or if it improved.

Don't be upset, you didn't just lose a long, concise explanation like I just did.

[Medyo Bastos]

Do you have the correct advancer?


Sent from my iPhone using Tapatalk

[TwoTired]

Are you saying the socket for the advancer dowel has elongated?

Then I suggest finding true TDC crank position, as the ones on the advancer aren’t true anymore. Grease or better yet find mold release, carnuba wax and apply both wax and release to the pin and the advancer mount surface.  Clean the socket in the crank with alcohol.  Mix up some JB weld to put in the crank hole. Then install the advancer with the timing mark aligned with the TDC mark on the case and let cure.  This should “recondition” the socket.

I’ll try to find an earlier post I made about the points plate slop in the bosses to cure running out of timing slot and re post it for you.  It was a long post.  You’ll need feeler gauges.

[PeWe]

I'm sure that you will get it right if move advancer to fully counterclockwise, then tighten the M6 nut (10mm wrench)
Both my CB750 have an advancer play of 3-4  crank degrees when the M6 nut is not tightened.
'T' on advancer match mark on case when advancer is moved fully counterclockwise.

Checked when head is off, using piston stop with head on, screwdriver thru plug hole.
(There are a few crank degrees where piston does not move up-down. Important to define the center which is easier with piston stop without rocker arms moving valves.)

I have made an additional case mark (3mm after stock mark) on my K6 to use when timing cam and I rotate crank by a 23mm wrench on the big nut. Risk that advancer moves.

Both advancers have cut springs to keep advance to not happen too early.
My K6 stock advancer, TEC 300 had a horrible play where springs did not held weights.

My K2 with TEC 300 advancer could not get F to match mark at idle, it was 1 mm advanced. Cut springs fixed it.

My K6 has now an Hitachi advancer, same with that, cut both springs to ensure F matching mark at idle 1000-1200 rpm.

[Alan F.]

Here's a screenshot of his advancer from the video showing the slop, from appendix G-2 in HM's book it'll be a Tec brand noted by the fat advance arms.
It's a '300' advancer if you can't see the photo.

[YoungBlood]

I am becoming superstitious about this all, but that explanation is for another day. Here's the symptoms after yesterday:
Before leaving to see family, I did the camchain adjustment. I double checked the valve's, only adjusted one valve, a touch tighter since I was doing the over-gap method with a .025 and .04 feeler. I checked the timing, all was lined up. I put the 105 main and 40 slow back in.
- At my destination I checked the timing, 1/4 is at F when contact breaker arms lift away. Same with 2/3. I do static timing with a 6 - 12V test light which I hook the alligator clip to the green condenser, or the nut on the end of either 1/4 or 2/3's contact ear. I rotate the crank with an adjustable wrench since I was away from home without 23mm. I find when the light turns on for 1/4. Then adjust if I need to. Everything is spot on.
- I check my oil later that night, and 2 quarts low! Obviously I filled it up, but the hesitation got really bad. Stupid, I didn't know where it went, and wasn't as cautious as I should have been. It's probably been a few weeks since I checked. I did an oil change ~1000 miles ago and was checking oil often without a noticeable loss, if any!. Yesterday was 95 degrees, humid, and I was stuck in traffic... It is leaking out of the alternator cover, head gasket, and now the valve cover.
- There is a hiss coming from the carburetor, valve leak?
- I went to Home-Depot thinking I could find some brass-paper, I could not. I reinstalled the advancer and noticed that the dowel is perfectly circular, so is the crankshaft dowel/pin hole. No elongation, sorry 2Tired, I was dehydrated yesterday. I believe I set it to fully counter clock wise, which would advance the timing from where I was before, no?
- Bike wouldn't start, the 1/4 contact breaker arm arced heavily, basically ground out. I was worried I was stranded away from home. I put new plugs in.
- I check the voltage at the blue 1/4 wire. 10.3 volts. At the 2/3 wire I was getting like 10.7 V.
- I get the bike running, big blue arcs coming from 1/4 points.
- Bike misfires home... badly, I thought the bike was about to see it's grave. It felt like the bike was running on 3, but wasn't, all four exhausts were scorching hot. Bike was fighting its self, felt like the timing was way way off.
- Did a plug chop, but phone died so I could not get pics of 1 and 2. Both 1 and 2 were black, sooty on the top. 2's porcelain was completely black. 1's porcelain was mainly black on one side, with some white, and brown on the other.
- Picture of 3 shows that it is hot, white. Picture of 4 shows it's completely carbon fouled.
- I become superstitious, I get back into Chicago, because suddenly the hesitation disappears. What the hell? Bike pulls evenly, and smoothly with 1/8 - 1/2 turn of throttle. A solid sound to an engine, clean, happy. Beyond 1/2 turn bike starts to choke up, I believe around 4k range. Not sure, my tach cable broke a few weeks ago.
Here's what I am thinking. I have more than one problem going on, and likely they are all adding to the difficulty for good engine performance. Power is being intermittently broken somewhere as Twotired said. I am going to look for that problem, but first I want to see how the bike is running when I go and start it. If it's bad again, I'll hunt on the electrical connectors and get some readings to you all.
Pull off the air screws, put the Keihin stock ones in. Pull the timing plate, pull the advancer off, and triple check that it is set fully counter-clock wise in the dowel hole. Reassemble, and do static timing with a video so you folks can see my method and make sure I'm not doing this wrong?
I'll try to do a compression test, I need a 12mm adapter for the gauge. Autozone doesn't have it, maybe O'reilly's. I tried to do a compression a couple days ago but the rental tool doesn't have 12mm. I'm worried about a valve leak, no idea how to get a 100% confirmation other than the high hiss at idle from what the Honda manual says.
Order TEC ears for 1/4 2/3. I start my college summer job on my b-day tomorrow, so I should be able to afford more stuff I need.
I would like to buy a strobe light, money's tight, but I would like to figure out if that advancer is working properly, and dial in the timing perfectly.
PeWe, I've got a 300 TEC, I'm not sure how to find TDC without use of the advancer's markings. I understand what you're saying, but I believe you're letting me know fully counter-clock wise is TDC, you checked? So I am going to set it fully counterclockwise thinking it aligns with TDC.  Are you also saying that using 23 mm to rotate the crank runs the risk of pull the advancer clock-wise?
TwoTired, what do you mean the TDC mark on the case? I only see the index mark. Will take a look soon. Here are the plug pictures: https://drive.google.com/drive/folders/1pEvFQOprsEYFT9ccQ6IUhKbsfnUFvbbG?usp=sharing
Here is a video of the arcing on 1/4, and a melancholic engine noise : https://drive.google.com/file/d/1sESTgDLk9UF95ATmJEEElld3jsa42cY2/view?usp=sharing

[Alan F.]

Well, happy birthday anyway.

[YoungBlood]

25 years! Thanks Alan, and thank you everyone for the great advice. My apologies for missing a few things people have said, and not following all advice to a T, a lot of things to keep track of.

[YoungBlood]

The old needle pictures. No Keihin “K” stamp, they have 271307 stamped.