Honda Twins banner
1 - 14 of 14 Posts

·
Registered
Joined
·
55 Posts
Discussion Starter · #1 ·
It rises and falls, I'm trying to get it around 1200-1300 and it will stay there for a bit but then it could rise to almost 2000 or drop to 1000, at 1000 rpms its very close to stalling and I've got to get on the gas to bring it back up, the right side exhaust seems to heat up a little faster and runs hotter. I'm confident every thing is correct, valve clearance , timing, points gap, compression, carbs are cleaned with new o-rings. I do seem to have a very little bit of an exhaust leak on the right side, where the head pipe meets the engine, also a couple of rust holes all the way back on the right side muffler. Also on my left side intake boot I have a crack but I'm sure it doesn't go through, I've cleaned the surfaces well where the intakes mount to the engine and replaced the old clamps to get a good seal at the carbs. I seem to get no-where whem I'm adjusting the idle mixture screws, small adjustments seem to do nothing and then I give up turn them back in and start again, usually at around 3/4 to 1-1/4 as a start. Any ideas would be appreciated. Thanks.
 

·
Registered
Joined
·
30 Posts
Definitely fix that leak at the exhaust manifold. The little copper gaskets are readily available. Then make sure the carbs are synchronised. It sounds very much like they are out. Try one thing at a time.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #3 ·
You mean those little copper gaskets that weren't there, it really was a very minor leak so it was sealed pretty good I guess without them. Going to pick a set up tomorrow and then try another run before I touch the carbs again. Thanks
 

·
Registered
Joined
·
363 Posts
twinz said:
Definitely fix that leak at the exhaust manifold. The little copper gaskets are readily available. quote]


When I took my pipes off the first time, there were no copper gaskets. I put it back that way it was an it was fine no leaks that I know of. My question is: How important are the copper gaskets? It seems to me that there wouldn't be a good seal with them but that's just me.

Matt
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #6 ·
tbpmusic said:
..
..
.

You need to tell us the year/model you speak of.
Take your compression readings, too - let us know that info.
Sorry, it's a 73 cb350, a barn rescue that I've been working on over the winter.

I did the comp. test cold, got a tick over 155 right and 160 left, I posted a question here last week and was pretty satisfied these were ok numbers, the shop manual says 170 psi on a warm engine.
 

·
Registered
Joined
·
6,495 Posts
If adjusting the mixture (or "air") screws gets no response at all, somethings wrong.
Could be a host of causes - maybe the screws themselves are deformed or buggered.
Maybe the carbs need a good cleaning.
How about the diaphragms.
And test for air leaks, don't just assume it's ok.
Exhaust leaks in general are discouraged.
To find intake leaks, I carefully "spray" a propane torch (unlighted) in the general areas - if there's an intake leak, you'll hear the engine speed up.
Or it could be that they're not quite balanced/synched.
Or the timing could be off.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #8 ·
tbpmusic said:
If adjusting the mixture (or "air") screws gets no response at all, somethings wrong.
Could be a host of causes - maybe the screws themselves are deformed or buggered.
Maybe the carbs need a good cleaning.
How about the diaphragms.
And test for air leaks, don't just assume it's ok.
Exhaust leaks in general are discouraged.
To find intake leaks, I carefully "spray" a propane torch (unlighted) in the general areas - if there's an intake leak, you'll hear the engine speed up.
Or it could be that they're not quite balanced/synched.
Or the timing could be off.

I'll try the propane trick tomorrow when I get the exhaust back on with the new gaskets, I've done the propane(kinda scary)thing before but not yet on this bike. Thanks
 

·
Premium Member
Joined
·
1,374 Posts
gut feeling I'm going for intake leak -head to carb especially if she takes longer than normal to drop down to the 1000rpm before she sounds like she will stall.Bin there done that -got me stuck once after checking everything else was correct.Regards Chris.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #11 ·
Hey, first off thanks for advice and links to the manual, I've had the shop manual downloaded for awhile

Anyway, I got my exhaust gaskets and it finally warmed up enough outside (just hit 0 C) to take it out to start, I did the propane thing early just a few minutes after starting after it would run nice off choke, sprayed around the intake manifolds and throttle shafts with no differance in rpm. Once fully warmed the idle fluxuations are alot better, not sure how accurate the old tach is but it seems to sound good idleing around 1400 and it'll stay pretty solid but still bounces up and down maybe 100- 200 rpms each way, so it's an improvement. I think I'm going to leave it now and start riding it before anymore adjustments. Kinda try and fine tune it from there.
 

·
Registered
Joined
·
6,495 Posts
You should be able to idle steady at less than 1200 rpm.

Are you still getting no response from the mixture screws??
If so, then clearly the low speed circuit is not working.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #13 ·
tbpmusic said:
You should be able to idle steady at less than 1200 rpm.

Are you still getting no response from the mixture screws??
If so, then clearly the low speed circuit is not working.

It will run at 1200 but not steady, if it drops to 1100 or less then it comes close to stalling. I gave the left mixture screw about 1/8 turn out from where it was, took the right out probably 1/2 over a couple times but ended up almost back where it was, maybe 1/8 out from where I started this time, seemed to help some. I can see how it takes an experienced ear to adjust these. Things seem balanced out better, exhaust pulse and heat, it revs nice with a quick crack of the throttle, no bogging, and the revs come back down good, I'm getting a few pops after a rev up when its comin down, as best as I can tell by myself these pops are from the right side. All in all I'm happy with the improvements, one kick started it today stone cold and it will sit and idle forever if I set it at 1400 rpms, it just goes up and down by 100 to 200 rpms.

So if the low speed circuit is not working is another carb cleaning the answer? Thanks
 

·
Registered
Joined
·
6,495 Posts
1 - 14 of 14 Posts
Top