Is a 150 main to big?

Well... I doesn't want to run good with the choke off. I have to back out the mix screw about for or five turns. What's that mean? Should I take out the 32.5 pilots and try the 30?

Posted via Mobile
 
Your plugs could be black from using the enrichener to support the system. You have to work with the mixture screw and pilot alone, or you taint the results. If you are pouring that much fuel at it, you surely have intake leaks.
 
You have to keep all other things equal and try to change one thing at a time. Put your filters on every time. That's the way you are going to ride, right? Running with the enrichener on is not running correctly. It's seldom needed for more than 30 seconds on a cold start with these bikes. Often much less than that. Mine will only run with it for about 10-12 seconds before it starts to rich stumble and wants me to close the enrichener valves.
 
Michaelrupp1, yes I should have made it clear my 76/77 BS38s run up from stock on 135s and 27.5s - my 78/79s I am putting in 30s or 32.5s and going with 140 as my first experiment on those (advice from 5twins, of course).

You will get there, it's just a matter of experimenting, and having various pilots and mains at hand.

Anlaf
 
Well I changed to 30 pilots and it runs good with the choke off but when I give it gas it pops loudly! Scared my dogs. Do I need to turn the mix screws in or out. I don't think I can ride it very long to check the plugs

Posted via Mobile
 
The popping might just be the carbs are out of synch with each other (synch srew to adjust).

Popping can be loose exhaust headers, or leaks around the carbs.

Popping can indicate a lean mix, too. What are your current stting - 2.5 turns out, I presume?

Anlaf
 
ANLAF said:
The popping might just be the carbs are out of synch with each other (synch srew to adjust).

Popping can be loose exhaust headers, or leaks around the carbs.

Popping can indicate a lean mix, too. What are your current stting - 2.5 turns out, I presume?

Anlaf
Click to expand...

I have the mix at 2.5. Turned in some, turned out some... No better. When I tighten the manifold clamps it want to push the carb off.

So I am now running 140 mains and 30 pilots needle clip is in the number two position from the blunt end.
It's is when I get frustrated and put it away:mad:

Posted via Mobile
 
Let me ask this, since it ran good with the choke on and the 32.5 pilots and when I put the 30 pilots in it didn't run good it popped, should I put the 32.5 back and change the needle setting, up or down? I was closer than I have been with the 32.5 and a 140 main.
Any advice
What is the best manifold clamp style?

Posted via Mobile
 
The pilot is part of the idle control - when you say you run it and it pops, is this at idle or giving it some revs, say 2500, 3000 (mid-range)?

If it is idle, then popping indicates running a little lean, so turn the screw out - the mixer screw is part of the idle control combination.

If the popping is mid range it will be to do (but not solely) with your jet needles (the slides come up and down in mid-range). This is likely to be that your carbs are out of sync with each other (as mone was yesterday until I tweaked). Now, all things being equal you should have started off with the butterfly valves on the carbs closed to the same degree (see my video for that). From the saddle you can turn the sync screw left to open a little the left cylinder, and vice versa (these things only need very small adjustments to make a difference). Remember where you started, and you can always return.

I have read the Carb Guide top to bottom now, and the above comes from that and me actually following the suggestions. Read the Carb Guide (5twins and grizld1 put in some time effort - read it, it is a great guide).

Hey, and don't get frustrated, be patient with these old dears. Use the stock clamps and make sure they close. There are other tests, too. Look at the Carb Guide, e.g. an easy diaphragm test, and a test to check there is no air leaking in, and a good test for the throttle shaft seals.

Anlaf
 
Your question on the clamps: Use what holds them firmly in place. If they are squirming under the standard clamps then use a hose clamp, but it MUST be firm and consistient.
How you go from a 32.5 and needing the enrichener to idle or run to a 30 pilot and no enrichener is by sealing up a decent sized leak. Like I said before, the goal is to keep all other things equal as possible and only change one item at a time. If you did not bench synch the carbs, you really need to. It will help you get your start and idle stable. I bench sync with a 1/8' drill bit in each carb throat at the bottom of the throttle plate. I let the throttle spring hold the drill bit at bottom center of the left one (I use the bleed holes as a guide to when I'm on the bottom) and adjust the sync screw until the other 1/8" bit will just slightly drag under the right side, but not enough to take the pressure off the left one.
 
Today is a new day. I used a home made manometer to sync the carbs. I got the as close as I can. It was a little bouncy. I did do the bench test before.

When I push forward on the carbs while its idling, the revs would change a little. I don't think my clamps are doing a great job. I may try and get the band style clamp. I don't know what came from factory. My manifolds are brand new with new gasketsi did spray some carb cleaner around the manifolds while its running to see if the revs change. No change.
You guy have great advice, please keep it coming!

Posted via Mobile
 
Do you have new JBM clamps or new Mikes? Mikes rubber products are not known for quality. Pushing the carbs forward and having the rpm change could be a sign of a leak, but could be nothing, depending on how much you can move them.
 
Last edited:
Your comment about the carbs squeezing out when you tighten the clamps has me thinking maybe you haven't seated them into the manifolds fully. They should be pushed in pretty much as far as they'll go, until the round castings for the butterfly shafts and the mix screws are practically touching the manifold, casting on the bottom for the angle bracket too .....

FullyMounted.jpg


Also, if your new manifolds are not from JBM, you really need the metal shrouds over them or they're going to split in short order.
 
My experience with Mikesxs carb intakes (manifolds)..................they are sub standard. They did not fit properly, as they are manufactured to the wrong size, and I had air inleakage that could not be cured. I changed back to my OEM 35 year old manifolds, and they work perfect...............still using the stock OEM ones.
 
Well I thought I would go back to the 32.5 pilots and work from there.
What I notice that is not correct is the 32.5 or is different is that the 30's
Are open on both ends. The 32.5 have a very, very small hole in the bottom. Could this be one of my issues.
 

Attachments

  • image.jpg
    image.jpg
    153.5 KB · Views: 159

Similar threads

JNaw
More carb/power issues/questions
Replies
6
Views
160
5twins
5twins
C
Running rich. Main jet size?
Replies
6
Views
235
Melnic
M
ForestHasAnXS650Too
New-Old XS650 Journey - Carb exploring and wrong parts, pointers?
Replies
6
Views
214
5twins
5twins
B
XS650 BS34 CARBS
Replies
2
Views
253
BACK SHIFT
B
H
91 octane or 87 octane for 1972 XS2 with Mikuni carb conversion??
Replies
5
Views
340
Signal
Signal
Back
Top