Rebuilt carbs, add airfilter:engine dies?????

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Jul 24, 2005
Hey guys, just finished rebuilding a set of 932 Amals. The old carbys had no pilot jets in them, which i thought was quite weird, but those carbs ran ok on the bike, so I didnt think much of it. On the rebuild job, I got nearly new bodies and slides, I reasembled them, this time with some pilot jets. I mounted everything back onto the bike, left filter off because I intended to spray some carby cleaner in them just in case I misssed some dirt on rebuild. The bike ran great at a stand still without the filter, revved great, still gotta work on idle, took her on the road for a second, midrange(needle) is too lean, but filter was off so...... I put on filter, and TRIED to crank it up. It would not crank, untill I held it at half throttle, when I got it running, it would run at no less than 1/4 throttle (pilot circuit, I think?) Took filter back off, ran great like first time, left it running, tried to put on filter, when there was no gap between filter and carb mouth, bike would die, unless I was over 1/4 throttle. Screwed in pilot screws at max half a turn. On rebuild I raised clip one notch because she was running very rich, put in 220 mains, 106 needle(stock), it has to be the fact that I put in the pilot jets, yes??????? :?: 72 Fastback Combat
The concentric carb mostly came with no screw in pilot jet but with a preinstalled pilot bushing, this makes it seem like there is no pilot jet. Looks like you now have 2 pilot jets in there now, but that really shouldn't matter as long as the new ones you added are the correct size or larger as the smallest one fitted will be the governing one.

What your main problem is it the changes required to key in your new carbs, they will behave differntly because you no longer have the variable air leaks you get with worn carbs. What will have happened is that over the years as the carbs were wearing the mixture leaned off, the settings were richened to get the bike running so with new unworn carbs and the same settings you get a rich mixture. Anyway here is what I would do.

1. Take your extra pilot jets out, but make sure the pilot bushes are there first. The pilot bush is always equivalent to a 25 pilot jet.

2. Use carb cleaner and double check the pilot circuit is clear.

3. Put your Jets/needle settings are as per the book for your model.

4. Start the bike and tune the idle.

5. Take the bike out and tune the needle postion and the main jet.

6. Tune the idle again.
When you put on the air filter are you sure it is not covering the air inlet into the carb body. The hole for the pilot circuit comes in from the air filter end and if you are not using a stock filter, might be covering this over. If it gets blocked regardless of what you do to the air screw it won't change. Might have a quick look to see if this is the case.
Steve J.
ok guys, I took out both pilot jets, which were 25's. Put it back together, cranked it up with no filter, and it runs great down low, whereas it didnt use to run nearly as good with the pilots in. So, I put on the air filter, which is a k&n which I cleaned and oiled, and the bike runs just as crappy as it did before i took out the pilots, i turned the pilot screw all the way in, all the way out, and neither seemed to improve much at all. I am stumped. all the carby settings are per book: 106 needle, top position, 220 mains, no pilots, WTF????? Also, while air filter was off, i ran it and then checked plug color, they seemed to be pretty good, probably a tad lean, white on the center electrode and black everywhere else, then put filter on and check plugs, horrible soot everywhere. The filter makes a noticable difference, like when revving w/o cleaner there is hardly any smoke from exhaust, put cleaner on, and there is lots of very thick black smoke, never thought a filter could make that much of a difference?
Your pilot jet / bushings are probably clogged. I don't undestand the air cleaner thing, but you have classic symptom.
Unscrew and remove the pilot screws, spray some carb cleaner, WD 40, something to loosen it up. Take single strand of 12ga. stranded wire, or strand of throttle cable or better yet a guitar G-string and poke around till you feel it go in. Spray again, poke again.
Reinstall pilot screws to 1 1/2 turns. Adjust accordingly.
Do you have fresh gas in tank?
Yes, just put in shell 93 octane, brand new gas. I will try to see if there is anything in the pilot screw hole, with a guitar string, then readjust, and I will tell you the results, thanks for the help btw.
Well, cleaned out pilot screw hole, nothing blocking it though. Took both pilot screws completely out of carbs, then cranked it. It actually idled, but if i gave it a little bit of throttle it would die, prob because of my rich settings everywhere else. If I hold my finger over the hole, it seemed to slow the idle, indicating a richer mixture I think. However, due to how rich the frigen carbs are with a filter on, i just fouled 2 plugs due to carbon, so now I have to get new plugs, then i will put something over pilot hole, then see how it runs. Any ideas on how to fix this problem??? I ran it with #25 pilots in, and screwed pilot all the way in (richest), and it still ran crappy, wut is there to do????????
It's tough to diagnose this at the computer so lets start with a little background.
There are two types of 932's. The 750's ran a straight spray tube, the 850's ran a cut away spray tube. I wouldn't worry so much as to which one on which bike at this point, however the needles need to be matched with the spray tube.
The straight spray tube uses a needle with two rings, the cut away tube uses a 4 ring needle. These marks are above the circlip grooves.
Also, usually the 850's run a 3 1/2 slide, the 750's run a 3.
I would start with needle in the center groove.
Make sure the choke is fully OPENED. I remove the chokes all together on my bikes.

Check back , I am interested to see how this turns out.
The carbs I originally took off were the originals i think, they have the float bowl drain screw on the bottom, they are 932's. The ones I put on I am unsure of wut they were on but they are 932's without the float bowl drain screw. The originals had a round bronze piece in center of carb (looking from top), the piece was only half, whereas the ones I put on had a whole circle brionze thing, I am assuming this is the "spray tube"?? I also did notice different needle lengths between the two carbs, the originals were either longer or shorter(dont remember) than the carbs I reinstalled. On rebuild I put in the longer needle because I needed a leaner mixture, and I put the clip in the top position. The original carbs had clip in middle position.
With air filter on, bike will only run with pilot screws removed, w/o filter it will run best with screws all the way in almost, hell of a difference, I know. Overall with filter on it runs very very crappy, lots of black ex. smoke and smell of unburnt gas. Without filter hardly any black ex. smoke and revs great, other than mid being lean, which is understandable. Sorry if i already posted some of this info.
I believe the needles are the problem. The lengths are diff and the diameter also. Match up the correct needle with the spray tube, yes, that bronze thingy in the bottom of the carb throat.

If that doesn't correct it, check float level next. Float level may be too high. You can simply change out bowls with the previous ones that worked.
the original carbs had the rubber tipped brass float needle, and the carbs i put backn on had the nylon float needle, I guess I will swap them and try that. Thanks for the help, I will let u know how it goes.
Hard to be of much help on the computer. I had similar carb problems that neither my dealer or me could figure out. Finally I dismantled the carbs and put in new (chrome) slides, needles, jets etc, but everything as stock, including float level. Started first kick and has run like a clock ever since. I bought a guitar string to clean out passages, just use care.

Sounds like your carbs have been played with making it almost impossible to sort out. With factory carbs and settings these bikes ran very well.
I just took off the carbs that I recently put on the bike, and they had needles with 4 little notches at the top, 850 standard needle i believe? Anyway I put in the needles with only 2 little notches at the top which are standard for a 750 I think. Put clip at top position as per riders manual. I took it for a quick spin and it runs even worse than before, if I go WOT it pops and the power jumps in and out and never really clears up. This condition could be either way lean or way rich, so i thought. I pulled plugs and they were extremely sooty. Also at tickover u can see puffs of black smoke just pissing out the exhaust. One question, of the two carbs I have the originals had longer pilot screws than the others, I am running the shorter ones, which was standard 750? After this experience, the only thing i can narrow it down to is frigen float height(i will check it tomorrow), can anyone give me a baseline of where to start? The lower the height the leaner correct? I am assuming that its possible to entirely ruin a carbs tune if the float height is wrong, i mean i have 220 mains and all my tests are conducted w/o airfilter and its rich as hell. with air filter on (k&n) the engine will die below about 1\4 throttle and when u give it gas it smokes like a semi. Can anyone who lives at or 1000ft above sea level and has 60-90 degree fahrenheit temps post their carb setup??? thanks in advance, and appologies for the long post
I have become convinced that a #78 drill that is .016 thick is the only right way to clean or check these jets. You will need a pin vice or a small brass tube to crush the drill into to hold on to this very small drill. But by simply turning it in slow you will bring it back to it's size no matter what's in there. They are cheap buy a few.
OK guys, after a long while I took off the float bowls, put them in steaming hot water, and adjusted the float height. As of now the float height is so low that the carbs will not tickle, no matter how long you hold them down. i figured this would make the bike run leaner than usual, which would be a dream come true. However, it did not, 95 degree heat, no choke, fires by about 4th kick(bear in mind I dont run any battery). Ran it a little bit, still with no air filter, check plugs, and to my surprise they are still a very sooty black. I then left engine running, and put on the K&N Filter and it proceeded to kill the engine, unless I gave it throttle, and with large amounts of throttle it blows a decent amount of dark black smoke out the exhaust. WHAT THE HELL??? What is left to do now, the only thing i can think of is replace the needle, and drop main from my current 220 down to a 200 or something??
Hi Fastback

How frustrating is this, you said in your post on the 19th. of May if you gave it a handfull of throttle it would pop and carry on, i was wondering if your ignition timing may be astray which could be adding to your problems.

Sooty plugs definitely means it is to rich but if you find any small fragments of alloy on the plugs around the porcelain it may be a sign of pre-ignition.

Ihope you get it sorted.

Well, I am running a Boyer, so i am assuming that the timing is fine, never been checked though. As far as the popping goes, its more like sputtering, I think its just from way too much fuel, but I understand where your coming from. Whats the easiest way to check the timing with a boyer?
Hi Fastback

An earlier reply asked you if you had closed the choke (amongst other things) - have you done this?

Remember to close the choke for normal running you have to pull the choke lever so that it is 90 degrees to the handlebar to PULL the choke slides UP the body of the carbs (and therefore stop them choking the carb).

In my innocence I was caught out getting the lever position wrong when I first got my Commando :oops:
Timing is set with strobe. A Boyer is set @ 31 deg @ 5000 rpm.
It certainly sounds like carby issues, but I would make sure everything else is in check, IE valve adjustment, timing , battery condition, plug type, connections, both plugs fire etc.

Then verify carb slide sync and choke operation. Twist open the throttles fully, the choke should not be exposed at all. If it is down at all, it is blocking air.
When i first messed with the bike I ran the choke backwards on accident, but now I know how it works. When i syncronized the carbs, I made sure that the chcokes were not exposed while at full throttle. I am running Champion n7yc plugs and sometimes the NGK BP7ES. Quite some time ago I decided the check the valve clearances. I found that the clearances were set to a standard engine (6 thou intake 8 thou exhaust), with the exception that the left ex. was way out of whack, something like 23 thou. So I set them to Combat clearances, and it didnt seem to start as well. i know my engine has a high compression head(clearance between where the head and barrels meet is less than clearance between two engine cooling fins), which designates its a Combat, and it has the black barrels, but this has led me to believe it may not have the Combat cam in it. Should I change the clearances back to standard specs, and see how it runs then?? NO ALLOY on plugs, in response to mike mcmanus
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