Topic: 1977 CB750 K7 Resto-mod, Knoxville

[SOHC4 Cafe Racer Fan]

Yep. I've done that too.

[AintNoEasyWay]

Well, rode the bike a few times in the past two weeks, but I'm back to the same problem again with throttle twists killing the engine. The bike will also only hold idle for about 15 seconds or so then die out if I push in the choke. Before it would at least hold idle until I twisted the throttle. I can only assume that the problems are getting worse or creating others.

So carbs were back off again last night. I went ahead & adjusted all the floats to 12.5 mm down from 14.5 so it's not a question anymore. Pulled the pressed in slow jets & cleaned with carb cleaner, along with the main jets & pilots. All the accel pump nozzles are shooting gas well.

I didn't try firing the bike back up last night after putting everything back on, but I did replace my old spark plugs. I looked down into the cylinders & it looks like my pistons have a lot of grime on them already. I'm worried I've got something wrong & don't want to do serious damage to the rebuilt engine if so. I'm considering taking it to a repair shop outside of Knoxville that does vintage motorcycle repair (same shop that I had set up the valves & do machine work for me) to have them check everything out.

If you guys have any more ideas for what I could try, please let me know!

I am running a MAC 4-1 exhaust with stock air box.
- 110 main jet
- 35 slow jet

I used this kit to rebuild my carbs: http://webhosting.web.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://www.cycleonemanufacturing.com/sitebuildercontent/sitebuilderpictures/sir.kh1156nfr.jpg&target=tlx_pic25dr

The clip on my jet needle is set one down from top. Pilot screws 1.5 turns out.

EDIT: Looking here: http://www.salocal.com/sohc/tech/carb/asmpg_mgs/jetgraph.htm, he lists the K7 as having a 115 main jet, but I'm pretty sure my rebuild kit came with 110s so that's what I'm using now. Maybe that's why I've been running so lean!? Any recommendations on what to move up to?

[madmtnmotors]

I don't recall whether this has been addressed, but what condition are the carb to head rubber manifolds in? Are they old and hard and cracked? Sounds like there could be some vacuum leakage.

Also, check the points plate (or Dyna plate, or Pamco plate, etc) and make sure the three attachment screws are tight. The ignition plate is grounded to the engine through the metal backing plate and I have had these rattle loose (or forgot to tighten them  ) and have had the ignition cut out as a result.

[AintNoEasyWay]

I don't recall whether this has been addressed, but what condition are the carb to head rubber manifolds in? Are they old and hard and cracked? Sounds like there could be some vacuum leakage.

Also, check the points plate (or Dyna plate, or Pamco plate, etc) and make sure the three attachment screws are tight. The ignition plate is grounded to the engine through the metal backing plate and I have had these rattle loose (or forgot to tighten them  ) and have had the ignition cut out as a result.

Interesting. I replaced the manifolds from the air box but am still using the original boots between head & carbs. They seem to be in good condition with rubber not cracked or hard at all. I haven't tested for any vacuum leaks. Maybe a good thing to check.

[Restoration Fan]

You know how to check for vacuum leaks, right?

[AintNoEasyWay]

You know how to check for vacuum leaks, right?

I only know how to check it if I can get the bike to hold idle -- by spraying the boots & seeing if RPMs increase. But if the bikes won't hold any idle, I'm not sure of another method.

[madmtnmotors]

Look at the clamps on the boots. If they are stretched/bent then make sure they are not "bottoming out" before getting tight.

[RAFster122s]

It really does not take much of a leak prior to the head on a carb to really throw off the idle. If the boots are a bit too loose/large they will clamp down but leak. Just like a fuel line that's too large will weep or drip.

[AintNoEasyWay]

Look at the clamps on the boots. If they are stretched/bent then make sure they are not "bottoming out" before getting tight.

Also a very good suggestion. Thanks, madmtn. I've replaced 8 of the clamps and they have done great, but the last 4 clamps (between the engine and the manifolds) are original & may have been bent at some point.

[AintNoEasyWay]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

[Bigsam302]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

I got just the place.  Try www.vintagecb750.com.  They are in Canada and they make reproduction boots.  I just picked up a pair and they work well.

Sam

[AintNoEasyWay]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

I got just the place.  Try www.vintagecb750.com.  They are in Canada and they make reproduction boots.  I just picked up a pair and they work well.

Sam

Hmm, looks like they only carry the carb to airbox rubbers.

[Bigsam302]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

I got just the place.  Try www.vintagecb750.com.  They are in Canada and they make reproduction boots.  I just picked up a pair and they work well.

Sam

Hmm, looks like they only carry the carb to airbox rubbers.

You are talking about the rubber intake boots that go from the cylinder head to the carbs, right?  I just checked their website and they do have them for your bike.  They call them carb holders.  I ordered a set from them last month to fit my Mikuni carbs.

[SOHC4 Cafe Racer Fan]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

I got just the place.  Try www.vintagecb750.com.  They are in Canada and they make reproduction boots.  I just picked up a pair and they work well.

Sam

Hmm, looks like they only carry the carb to airbox rubbers.

You are talking about the rubber intake boots that go from the cylinder head to the carbs, right?  I just checked their website and they do have them for your bike.  They call them carb holders.  I ordered a set from them last month to fit my Mikuni carbs.

carburetor/intake/airbox manifolds/rubbers/insulators -- all the same

[Bigsam302]

Looks like Honda has stopped making the intake boots. Any advice on where to find reliable ones if I end up needing more? I've read on the site where guys had trouble with certain boots because they were cheaply made.

I got just the place.  Try www.vintagecb750.com.  They are in Canada and they make reproduction boots.  I just picked up a pair and they work well.

Sam

Hmm, looks like they only carry the carb to airbox rubbers.

You are talking about the rubber intake boots that go from the cylinder head to the carbs, right?  I just checked their website and they do have them for your bike.  They call them carb holders.  I ordered a set from them last month to fit my Mikuni carbs.

carburetor/intake/airbox manifolds/rubbers/insulators -- all the same

That's what I thought 

[madmtnmotors]

carburetor/intake/airbox manifolds/rubbers/insulators -- all the same

The airbox to carb rubbers are different than the carb to head rubbers...

[oldhatt45]

If you look at the fiche, the Carburetor to Head rubbers are called "Insulators".
Honda Part Numbers 16211-300-030 & 16212-300-030
I bought a set not too long ago (maybe a month or so) from JT Marks. 
jtmarks@hvc.rr.com

He is also a member of this forum I believe.
If I recall correctly they price for the set (there are 2 inners Insulator A and 2 outers Insulator B but I may have that reversed ) was $80.00 total for the 4 of them.

Charlie

[AintNoEasyWay]

carburetor/intake/airbox manifolds/rubbers/insulators -- all the same

The airbox to carb rubbers are different than the carb to head rubbers...

Mine are definitely not the same. Maybe they're referring to pre K7 bikes?

If you look at the fiche, the Carburetor to Head rubbers are called "Insulators".
Honda Part Numbers 16211-300-030 & 16212-300-030
I bought a set not too long ago (maybe a month or so) from JT Marks. 
jtmarks@hvc.rr.com

He is also a member of this forum I believe.
If I recall correctly they price for the set (there are 2 inners Insulator A and 2 outers Insulator B but I may have that reversed ) was $80.00 total for the 4 of them.

Charlie

Just what I needed. Thanks Charlie!

[enwri]

What did the plugs you took out look like? when you replaced them on the 16th.
The ones in the previous photos don't look lean, did they look burned clean after riding it around, or sooty.
one of them looked washed clean from unburned fuel.
 aren't they only a few weeks old, they shouldn't need replacing already, or are they the originals from before the rebuild?

[enwri]

What did the plugs you took out look like? when you replaced them on the 16th.
The ones in the previous photos don't look lean, did they look burned clean after riding it around, or sooty.
one of them looked washed clean from unburned fuel.
 aren't they only a few weeks old, they shouldn't need replacing already, or are they the originals from before the rebuild?

Mine will idle but not take any load if my needle is on the second from top , it has to be in the top  (leanest position) with mixture screws at 2 1/4.
Runs cleanly from idle to wide open. A lot of low speed running turns them black but burns off easily with a fast run.
I do have old worn slides and I suspect worn needles as well messing things up.

stock jetting, 4 into 1.

[AintNoEasyWay]

What did the plugs you took out look like? when you replaced them on the 16th.
The ones in the previous photos don't look lean, did they look burned clean after riding it around, or sooty.
one of them looked washed clean from unburned fuel.
 aren't they only a few weeks old, they shouldn't need replacing already, or are they the originals from before the rebuild?

Mine will idle but not take any load if my needle is on the second from top , it has to be in the top  (leanest position) with mixture screws at 2 1/4.
Runs cleanly from idle to wide open. A lot of low speed running turns them black but burns off easily with a fast run.
I do have old worn slides and I suspect worn needles as well messing things up.

stock jetting, 4 into 1.

Hey enwri, just replaced the plugs this week. Prior to that, I had in old plugs from before the rebuild. I can post pictures of them when I get home. #4 looks too white while the other three seemed somewhat normal. There was some wetness on 1 or more of the other plugs, if I recall correctly. They may be fouled, but I may not be experienced enough at reading plugs to tell.

I think I am going to break down & take it to the shop tomorrow to have them look at it. Missing out on crucial riding time before the cold starts up here in East TN.

[RAFster122s]

Fall is coming quickly here in NE TN,  the days are staying warm but,  the nights are turning cooler with temps down to 40s some and 50s usually.  That will change quickly in October.

Plug chop at speed will tell you more than just a ride and then pull into neighborhood & to home.
Just need a place to pull it over after shutdown where you can safely work pulling the plugs and swapping in a new set.
This way you can have multiple photos possible and you can capture conditions then and afterwards when cold. Wet plugs will dry is what I am thinking about.

Just about need a case of plugs when playing with jetting and the like. Or a good way to clean them for installing later.

David

[AintNoEasyWay]

Fall is coming quickly here in NE TN,  the days are staying warm but,  the nights are turning cooler with temps down to 40s some and 50s usually.  That will change quickly in October.

Plug chop at speed will tell you more than just a ride and then pull into neighborhood & to home.
Just need a place to pull it over after shutdown where you can safely work pulling the plugs and swapping in a new set.
This way you can have multiple photos possible and you can capture conditions then and afterwards when cold. Wet plugs will dry is what I am thinking about.

Just about need a case of plugs when playing with jetting and the like. Or a good way to clean them for installing later.

David

David, you're right. The cold is on its way for sure. All good advice, thank you. I am going to take the bike down tomorrow to Rising Sun Cycles in Harriman, TN to have them take a look at it. I'm afraid I'm going to do harm to the newly rebuilt engine if I keep playing with it myself.

[AintNoEasyWay]

Dropped the bike off at a shop last Saturday & got it back last night. Just needed a good carb sync & tune! Now this thing roars. Took it down the interstate & got it up at 80 a few times. That's the highest I've ever gone on a bike. Guys, I'm in love. These things run beautifully when fixed up properly. So happy I'll get to enjoy at least a few weeks before the cold comes in.

Here's a short video of it running:

It takes a few minutes to get it started & the guys at the shop confirmed these engines run a little cold, but once it gets started it runs great. Thanks for all the help, guys. No way would I have gotten this far without you all. I'll be back during winter to update as I rebuild the front forks, change out steering bearings, & get some new shocks put on.

[Restoration Fan]

She sounds great!  Well done, Nate!