Idle circuit problem

Oakland850 · Apr 10, 2011

My 74 850 has Amal 932 carbs that I can't seem to get right. They are new replacements, not worn out. The bike revs fine, but sometimes pops through the exhuast upon throttle release ( lean condition). The idle screws were always too far in ( 3/4 turn verses 1-1/2 turn) indicating a probable blockage in the fuel feed to them? I poked a .015 wire into the carb bodies after removing the screws - now the left carb has no idle circuit ( position of screw makes NO difference at all in idle speed or quality). Could I have messed something up in doing the wire poke thing? Where does the air come through for these idle jets? Is it one of the small holes at the bottom of the carb intake? Also, is there a way to clear them without removing the carbs? Thank again for all of your help guys.

MexicoMike · Apr 10, 2011

Sounds like a possible vacuum leak. Check the carb to manifold and manifold to head sealing and the rubber hose equalizer that goes between the two carbs.

Oakland850 · Apr 10, 2011

Yes - I checked that previously - even used propane gas from Bernz-O Matic all around that area - no leaks

bpatton · Apr 10, 2011

Oakland850 said:
Where does the air come through for these idle jets? Is it one of the small holes at the bottom of the carb intake? Also, is there a way to clear them without removing the carbs? Thank again for all of your help guys.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Here's a picture that shows the workings of the carb. The source of the air for the pilot jet is the small hole in the back on the air screw side. You may have forced something into the pilot jet with the wire. You could try using compressed air on the gas intake for the pilot with the air screw out.

DogT · Apr 10, 2011

With the carbs off, and the pilot screw out, get some carb cleaner with a long narrow tube and shoot it into the pilot screw hole. It should squirt out of the top inside of the carb and I think down into the bowl area. At least that will show you the ports are clean. If not, have to fix blockage. It's really hard to tell with a wire if you are getting past the mix chamber in the pilot. Read and re-read the JBA instructions, it will eventually make sense. These Amal carbs are very simple, if they are working right, other issues will confound you.

Dave
69S

Oakland850 · Apr 10, 2011

I found the problem but not the solution. With bowls removed, if you squirt air or carb cleaner into the pilot air screw hole, it comes out the the hole in the intake of the carb ( air inlet) . On the good carb, it also comes out the small hole which goes to the bowl to feed fuel - on the bad one, it is blocked. So, the fuel passage for idel is blocked. Tried compressed air, carb cleaner, you name it - complete blockage. Removed carb body - but on bench and still no go. There is a small aluminum plug in the carb body I assume to gain acces to this passage. Are thyey available if I remove this one? Cant even get a .010 guitar string throught it! :x

Diablouph · Apr 10, 2011

Looks like you are going to have to go to the drill bit on a stick. I have done it once, and it made me nervous. I'll bet it took me half and hour to do a three minute job. Read up on it, here and elsewhere. Make sure you UNDERSTAND EXACTLY what to do. Or, have someone who has done it before, help you. If you are a bay area guy, there is the Norton Club, and several shops which can be of help. I got my drill bit at Rabers ($10), but they are everywhere. Good luck.

MexicoMike · Apr 10, 2011

Yep - could be swarf or other junk from the manufacturing process clogging the passage. But whatever - it will have to be cleaned out. I've found it pays to treat new carbs (for cars AND bikes) just like old carbs and always assume they need cleaning/surfacing like carbs that have been sitting in the garage for the past 20 years...

Oakland850 · Apr 10, 2011

Diablough - Thats what it is looking like - what is the diameter of the drill bit and do you have a link to the procedure? Thanks

bpatton · Apr 10, 2011

Oakland850 said:
Diablough - Thats what it is looking like - what is the diameter of the drill bit and do you have a link to the procedure? Thanks

Bushman:
The pilot jet is drilled 16 thou dia. (0.016"), a very tiny orifice indeed. I use an old guitar string wire with a filed flat end to probe the jet from the air side, after the air adjuster screw is removed (use a flashlight to locate the orifice). Another useful tool is a #78 drill, mounted on an end of small brass or plastic tube, The drill will re-size the orifice, so be careful and make sure all swarf is blown out by compressed air.

DogT · Apr 10, 2011

bpatton said:
, so be careful and make sure all swarf is blown out by compressed air.

And put some carb cleaner through it so you can see it flowing. Those small red tubes on the end of the carb cleaner spray cans are good to hold the #78 bit, usually a .016 guitar string will do it though. Gauge how far you are through it by pushing it in and comparing it to the good carb. You can also just use your fingers when you think it's all the way through, and put it on the bottom of the body and see if it's past the brass cover. The holes are really hard to find, even with a flashlight, I've personally never seen the hole.

You can also do like JBA does and drill out the other side and make sure it all goes through, but then you need to plug the far side.

Dave
69S

Oakland850 · Apr 10, 2011

Found it! - The previous owner had put teflon tape on the threads of the pilot air screw ( apparantley he didn't think O rings work) which I cleaned off when I first looked at the carbs. Some of this was still in the orifice and when I poked it with a .016 guitar string yesterday, I pushed it into the orifice essentually blocking all idel fuel. What is amazing is that even 100 psi of air did not dislodge it, I used the #78 drill on the end of a hemostat and bingo - out comes the teflon - tough stuff, but not for use in fuel lines for sure. Moral of the story - don't play engineer - just put it back together the way it was made! Thanks for all the response - hopefully i can take go for a ride this week!

DogT · Apr 10, 2011

Glad it sorted and glad you told us. Good info.

Dave
69S

MelloYellow · Apr 11, 2011

Man, it is SO sweet to find the actual "smoking gun"!
I had the same problem: Amal 930 (pilot circuit blocked), used air, carb cleaner, a guitar string, and ended up boiling the offending carb body in water and Oxyclean for an hour - that finally fixed it.
Hope you got out for a successful ride!

MelloYellow

pete.v · Apr 11, 2011

I kinda went the other root. I cleaned my pilot with a 1/8 drill bit. That'll never get munged up again. I also got sets of screw in pilot jets(25.30.35).
Including this, I drilled out the blank end and added a cut off air adjuster screw with oring,
There is no longer a question as to the condition of this questionable pressed in jet.

swooshdave · Apr 11, 2011

pvisseriii said:
I kinda went the other root. I cleaned my pilot with a 1/8 drill bit. That'll never get munged up again. I also got sets of screw in pilot jets(25.30.35).
Including this, I drilled out the blank end and added a cut off air adjuster screw with oring,
There is no longer a question as to the condition of this questionable pressed in jet.

Which one did you use? I think the 25 is suppose to be right.

pete.v · Apr 11, 2011

swooshdave said:
pvisseriii said:

I kinda went the other root. I cleaned my pilot with a 1/8 drill bit. That'll never get munged up again. I also got sets of screw in pilot jets(25.30.35).
Including this, I drilled out the blank end and added a cut off air adjuster screw with oring,
There is no longer a question as to the condition of this questionable pressed in jet.

Click to expand...

Which one did you use? I think the 25 is suppose to be right.

With the new cammy I am using the #35. The need to up the pilot size made me do it. The real benifit was the new ease of balancing, even with the #25 to start.

Idle circuit problem

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