1 Cylinder hot, other one cold

[Capslocker]

Hello all

Like the tittle says, one cylinder is way hotter then the other one.

I've just rebuilt the top end of the engine. I've bought it almost completely in parts and pieces so i've never heard it spin before.
It started pretty much right away after the rebuilt and the engine turns okay.

It is my first engine built so I am kinda new in this

Any ideas? maybe carbs? (I didn't yet touched them as they seemed clean, and I haven't read the carb guide from the tech section yet)

 

[grizld1]

Ideas? Why, sure! The combustion tripod stands on three legs: ignition, compression, and fuel. Inspect in that order.

 

[wherearewe]

First i'd do a compression test if you can.

Then i'd give the carbs a clean and sync along with a new set of plugs.

 

[charlieyam]

whip the plug out on the cold cylinder and check for a spark; if Ok then fine if no spark try another plug, one you know is good, eg from the hot cylinder. If you dont get a spark then check the points are opening and closing and that they have power and you have power at the HT coil. Assuming the spark is sorted, then check the carb. start the bike does the cold cylinder cut in with the choke on. and stop when its taken off.Does it run the second cylinder if reved to say 4000rpm, if so strip and clean the pilot jet, clean the main as well.It may be that there are other issues but start with these simple checks most of the time its these at fault.. good luck...

 

[Capslocker]

The plugs and ignition are fine.
It is not that the cylinder doesnt warm at all, the other one is just way hotter. Sorry for the confusing title.
The engine revs quite good aswell. What i've noticed is that it only runs with the choke on. The moment i turn it off the engine stalls.

 

[retiredgentleman]

The plugs and ignition are fine.
It is not that the cylinder doesnt warm at all, the other one is just way hotter. Sorry for the confusing tittle.
The engine revs quite good aswell. What i've noticed is that it only runs with the choke on. The moment i turn it off the engine stalls.

Your problem area lies within the Pilot circuit, if you know what that is. Read the Carb Guide....................maybe read it a couple of times, until you understand what the pilot circuit does.

 

[Capslocker]

Thanks man
Reading it now. I'm not a native english speaker so I Will need to read it a few times before i fully understand it

Thanks for your help

 

[fredintoon]

Thanks man
Reading it now. I'm not a native english speaker so I Will need to read it a few times before i fully understand it
Thanks for your help

Hi Capslocker,
I thought we Canadians had a language problem until I checked Belgium on WIKI.
3 official languages, 9 regional dialects and a different keyboard layout, Oh my.
About the English, that's the title says. "Tittle" has a completely different meaning.
About the carbs, like they all said, clean them, clean them and clean them again.

 

[gggGary]

What year is the bike, what carbs does it have? If you are not sure, pictures will help us help you ID them.

 

[angus67]

My money is on sync.
So, what is a tittle? many 'titalating ' pictures in my head... just set me straight.

 

[peanut]

good luck

 

[Capslocker]

Hi Capslocker,
I thought we Canadians had a language problem until I checked Belgium on WIKI.
3 official languages, 9 regional dialects and a different keyboard layout, Oh my.
About the English, that's the title says. "Tittle" has a completely different meaning.
About the carbs, like they all said, clean them, clean them and clean them again.

Wait until you read about our political system
I do speak our 3 official languages and Some english. So I hope The english is any good and you all understand it?
"Tittle" is indeed not the right word for what i ment. So what about "i'm sorry for the confusing topic subject" ?

Anyway, i'll post Some pics of the carbs tonight. I don't really know from what year the engine is, i've got 3 different bikes from '77, '79 and '82 and they all came in boxes . Engine code 4t6, I thought that code went from 79-82?

 

[Capslocker]

Some pics:






Second pair of carbs: (this one i have never used)



And one Pic of the engine

 

[gggGary]

Nice pics but I think I see the problem....


Yup I'm sure of it, the motorcycle part is missing!!

set on the engine appears to be 76-77 BS38's

"extra" set appears to be BS34's

 

[Capslocker]

Oops no pics yet, keep trying!

Should be ok now.

 

[gggGary]

Sharp looking set up!

Would be nice to see a straight from the rear shot. All the CV carbs really like an air filter to run right. Foam Uni filters are prefered, pleated oiled tiny pods not so much.
In the US of A the carbs came with this jetting.

check that your jetting is correct or mildly oversized and matched side to side.

get into the carb guide, check for leaky floats, bad throttle shaft seals, and bad float valves, clean choke and idle circuits.
recheck valve clearances.
How are the compression numbers?
What do plugs look like after runnin for a bit.

 

[Capslocker]

Will check on that in the morning. I forgot to mention that the cylinders are bored to 750.
From what part do you like some more pics?

 

[gggGary]

looking into the intakes and between the carbs. While you are reading the guide, note the different bowls, jets used on BS38s and that they are not compatible.

 

[grizld1]

Heads up, here! The jetting specs 5twins and I listed in the Carb Guide apply to US models; jetting installed in European models may be different. What vacuum carbs really like is a still air box. If you must use pods, use the biggest ones that will fit the space, to minimize turbulence across the lower diaphragm chamber port.

 

[Capslocker]

Update:

Cleaned the carbs and now the engine is running fine with and without choke.
Both jets are 122,5 and the needle clip is positioned in the middle. Still, the right cilinder runs Verry hot verry fast, like 1 min after starting it is allready verry hot. The other Side is hot aswell but i can still hold my hand on the cilinder.

Both of the carb screws are out 1 turn. Compression test is about 110psi on both.

I did not had the carbs synced yet. Inside the carb of the hot cilinder the floating bowl has 2 small holes in it. Should i Replace the bowl?
Do you guys think it has anything to do with the cilinders temp?