Carb problem, i think ?

[cowboybob998]

It's early in the motning and i just got off work, this has been on my mind all night at work.
Right before i went to work about dusk i had my bike runing and was working on it, was trying to clean out the exhaust, had it reved up to about 6 grand, any way look down and the header pipes at the head were starting to glow red, this aint right, this is on a 4 to 1 header, what jets should i look at?

[DGXSER]

Well, your definitely running lean from the sound of things. Your pilot jets are smaller than stock, so I would definitely bump those to 42.5 or even 45. Your main jets take over in that RPM range though. I'd bump those up a size.

With the issue your having, I'd invest in a colortune plug. It will let you see if your lean or rich, and at what RPM. I do not feel it lets you fine tune to the exact perfect setting, I know a local member who can, but it is because he has done it so many times he knows how to compensate for the difference between the colortune and a real plug. It will help you avoid running that lean though, which can be very bad for your engine.

[planedick]

Colortune

A colortune will only help you set the idle mix. Anything wlse will require you to do the throttle chop and plug read to tell what is going on at other throttle settings or engine loads. Another thing, most aftermarket headers are not double walled like the stock pipes and will show heat much faster than stock pipes...

[cywelchjr]

I'll also mention that every manual I have read says to not run the engine at over 5k for any extended time sitting still. I believe it has to do with exactly conditions like this, you NEED air moving around the engine ANY the pipes to cool them to prevent damage!

[Jarion]

I'll also mention that every manual I have read says to not run the engine at over 5k for any extended time sitting still. I believe it has to do with exactly conditions like this, you NEED air moving around the engine ANY the pipes to cool them to prevent damage!

Have to agree.
Any air cooled engine running at speed (without air moving across it) will heat up.... I don't even like to let mine idle for long periods of time while sitting still.

[cowboybob998]

carbs

Well, your definitely running lean from the sound of things. Your pilot jets are smaller than stock, so I would definitely bump those to 42.5 or even 45. Your main jets take over in that RPM range though. I'd bump those up a size.

With the issue your having, I'd invest in a colortune plug. It will let you see if your lean or rich, and at what RPM. I do not feel it lets you fine tune to the exact perfect setting, I know a local member who can, but it is because he has done it so many times he knows how to compensate for the difference between the colortune and a real plug. It will help you avoid running that lean though, which can be very bad for your engine.

the carbs that are on there now came off an 81, i beleave they are stock but not sure this is a 78, gess i should change the info on what carbs and bike i am runing, nice day today wendy as you know what so think i will take the carbs off and look at them

[DGXSER]

The pilot jets are stock at 42.5 on almost all years, I think 78 may have been 45. Stock mains for 81 are 110 so 140 is huge!!

I think perhaps you want to look at the carb bodies and see if there are three or four holes on the inlets and if they have only Fuel Ts or both fuel and Vent Ts. At 140 mains those carbs should be about flooding out I would think if they truly are the newer or 81 model year carbs.

[cowboybob998]

The pilot jets are stock at 42.5 on almost all years, I think 78 may have been 45. Stock mains for 81 are 110 so 140 is huge!!

I think perhaps you want to look at the carb bodies and see if there are three or four holes on the inlets and if they have only Fuel Ts or both fuel and Vent Ts. At 140 mains those carbs should be about flooding out I would think if they truly are the newer or 81 model year carbs.

Yes the ones that are on there now are 81,i put them on there because they came off a runing bike, the ones that are listed on here are the ones i took off with the jets i have listed on here. sorry for the confusion
Yes i will look at the carbs but more than likely i will put the right carbs back on with the corect jets in them, gona need all the help i can get, thanks.

OH, should say that i got the 750 swap on it yesterday and took it for a short run and can realy tell the deference, not gona run it any more untill i get the carbs straighted out

[DGXSER]

honestly, alot of folks find the later model carbs easier to tune than those early ones. What jets are in the ones on there now? If they are stock jetting with the setup you have they could likely be lean then.

[Shacknasty]

Put a fan in front of yer scoot when workin' on it. Six grand makes a LOT of heat really quickly.

[petejw]

hi cowboybob998,

i noticed ur sig states that the floats are set at 25mm,
if those carbs are off an 81 model then they should be set at
23mm.
if u put the earlier carbs back on set the float heights at 25.7mm.

if ur going to run with pods, run the later model carbs as they dont have the vent
tubes and will be easier to tune.

also agree with the others its not a good thing to be revving an unloaded
engine at those rpms.

[cowboybob998]

honestly, alot of folks find the later model carbs easier to tune than those early ones. What jets are in the ones on there now? If they are stock jetting with the setup you have they could likely be lean then.

just checked the 81 carbs that are on there now and they are the stock jets, gona go with the early mod. carbs with 142.5 mains and 45 pilot, dont know why i had the piolots at 40.