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Discussion Starter · #1 · (Edited)
Hello again all,

I recently acquired a 1969 CB350 with Mikuni VM30s, 2-1 exhaust, and K&N pods.

Bike was stolen and is now since recovered.

The bike used to start easily and ran great, some issues at WOT (bog a bit), but that I didn't mind.

Now that I have the bike back it won't idle properly. I was able to get it to run a few times and take it out for a spin (30mins-1hr max). But now it won't idle at all. The left cylinder doesn't seem to fire consistently and the exhaust is much cooler than the right.

Carbs:

6F5 5th-clip Jet Needle
159 P-5 Needle Jet
15 Pilot Jet
165 Main Jet
2.5 Slides
2.0 Air Jet
1 Turn Air/Mix Screw

Misc:

- Compression (cold) - Left = 150 Right = 145
- Consistent bright spark on each plug
- Plugs would come out black after riding around a bit (after it was stolen)
- Hard to cold start/won't even start now

Here's what I've done so far:

- Cam chain adjustment
- Valves checked and have proper gap
- Points set with proper gap and timing set (static)
- New spark plugs with proper gap
- New Battery
- Fresh fuel

I'm hoping all this will get it running. I have some questions before I slap on the carbs and try to start it up again.

Right now I’m in the process of breaking down and cleaning my carbs. I noticed that one of the air jets was gunked up. After cleaning it, I noticed that the passage is clear, but the air jet is completely mashed in and I cannot remove it (looks like the PO tried to remove it, but got it stuck in the process and just cleared the passage).

Now the questions:

-Is it okay to slap on the carbs after they are cleaned and try to run the bike like this?
-If there's a difference between the carbs air jets will the bike run okay?
- Can I run the carbs without air jets and just have the diameter of each hole match?
- Should I try finding a new carb?

Any recommendations are appreciated!
 

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Sorry this seems to have slipped through one of those "cracks".

When an engine starts running differently, something has changed. You have pretty well eliminated everything but the carbs. That and the black (sooty?) plugs indicate that a cleaning/rebuild are a good next step. One of the 350 folks should be along to better advise but but the damage you describe may require a carb replacement.

FYI the "X turns out" settings for the mixture screws are just a place to start. From there, with the bike warmed up, they need to each be adjusted to achieve highest idle rpm.
 

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Discussion Starter · #4 ·
Sorry this seems to have slipped through one of those "cracks".

When an engine starts running differently, something has changed. You have pretty well eliminated everything but the carbs. That and the black (sooty?) plugs indicate that a cleaning/rebuild are a good next step. One of the 350 folks should be along to better advise but but the damage you describe may require a carb replacement.

FYI the "X turns out" settings for the mixture screws are just a place to start. From there, with the bike warmed up, they need to each be adjusted to achieve highest idle rpm.
Thanks for the reply!

I just finished cleaning the carbs and it looks like I’m gonna be able to salvage the one. I’ll post an update as soon as my gaskets come in and I’m able to try starting the bike up.

Do I adjust the mixture screws at the same time? Or do I do it one side at a time?
 

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Adjust the idle speed to spec.

Adjust one mixture screw to achieve highest idle rpm.

Re-adjust idle speed to spec.

Adjust the other mixture screw to achieve highest idle rpm.

After this it's best to do a dynamic carb sync, then repeat the mixture setting procedure.
 

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Your compression is LOW Min Spec is 150 below that is rebuild territory.

Change your oil - the Thief may have allowed Gas to dribble into the sump by NOT shutting off the petcock.

Maybe even try some SEAFOAM in the cylinders to loosen any carbon deposits on the rings and bring up the compression.
 

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Discussion Starter · #7 · (Edited)
Your compression is LOW Min Spec is 150 below that is rebuild territory.

Change your oil - the Thief may have allowed Gas to dribble into the sump by NOT shutting off the petcock.

Maybe even try some SEAFOAM in the cylinders to loosen any carbon deposits on the rings and bring up the compression.
Oil changed!

Will try some sea foam to see if that helps with compression. Any tips on how to do this?

In addition, those compression readings were take with the bike cold, no carbs. Will compression readings be better with proper temp?

Also, would it be okay to run my mikunis without air jets with my current jetting/setup?

Thanks so much for the advice!
 

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Discussion Starter · #8 ·
Hi guys,

Quick update.

Slapped on the carbs, fresh gas, fresh battery, new plugs, and all previous things mentioned in the post done. But nada!

Bike won’t fire up or idle at all, and the left cylinder doesn’t seem to be firing

I’m stumped...

I did manage to get it to fire up once, as long as I gave it some throttle. And then it idled for maybe 10-15 secs.

Took a look at the plugs and the left Still looked brand new. Right plug had some black on it as it was firing. Right exhaust was hot, left not...

Any advice???
 

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Do a leakdown test... but before you do, grab a can of starter fluid... shoot some into borh carbs, choke, and it SHOULD fire... if not.. your problem lies elsewhere. Possibly compression leakage (valves, rings, gasket), the leakdown test will give you a better idea. Or possibly spark... I have mentioned this before in another thread but I had s bad set of NGK plugs out of the box..
You said the plugs are "black" after a short ride.. either oil, or rich.. with the low conpression.. doesn't look good..
again do the leakdown test.. you will know what is what..
 

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Discussion Starter · #10 · (Edited)
Do a leakdown test... but before you do, grab a can of starter fluid... shoot some into borh carbs, choke, and it SHOULD fire... if not.. your problem lies elsewhere. Possibly compression leakage (valves, rings, gasket), the leakdown test will give you a better idea. Or possibly spark... I have mentioned this before in another thread but I had s bad set of NGK plugs out of the box..
You said the plugs are "black" after a short ride.. either oil, or rich.. with the low conpression.. doesn't look good..
again do the leakdown test.. you will know what is what..
Will try starter fluid and check spark over the weekend before I move onto the leakdown test.

I’m pretty sure my left cylinder isn’t firing. So I’m assuming it’s electrical? Any advice on how to check if that is the case (ie - coils)? I’m pretty confident with the mechanical aspect. But when it comes to electrical I feel faint.

Thanks!
 

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Discussion Starter · #11 · (Edited)
It lives!

Had a friend come by to take a crack at it and he got it running. Looks like the left carb was not flowing any fuel into the cylinder...:roll: Looks like I let them sit too long after cleaning them, that there was some white residue building up.

He did some tuning and adjusting so it does run now, but rich. He recommends I change the points as they are bit worn. Hopefully we get the bike dialed in the next time we work on it. I'll keep everyone updated.

Thanks for the replies/help everyone!
 
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