Problem with new Amal 930's

I just installed new Amal 930's on my 68. I've had the bike for a while but am just now getting around to getting it running. The right side carb does not seem to respond to the idle adjustment screw properly. The idle adjustment screw seems to need to be screwed way in to have any effect on the idle and the bike is not running right. I did the initial set-up the way I always have: 1-1/2 turns out on the air/mixture screws, 220 main jets, needle on the middle grooves, and everything sync'd per Bushmann's tips. The cylinder is definitely getting fuel and I did not find an obvious air leak.

Anyone have any ideas on where I should start to troubleshoot the situation?

Suspect plugged pilot jet &/or too low a float level.
1.5 turns out on propper ignition timing is goal Amal aim for.

Thanks Hobot. I figured maybe some swarf from Amal blocking pilot jet, but it's as clean as a whistle. I will recheck the float level in the morning.

Have you altered the fuel levels? There is information that supercedes the info on the Bushmans page here.

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=13

If you set new Amals to the 0.80" below the float bowl top setting they are likely to run weak.

maximini said:

The right side carb does not seem to respond to the idle adjustment screw properly. The idle adjustment screw seems to need to be screwed way in to have any effect on the idle and the bike is not running right.

Anyone have any ideas on where I should start to troubleshoot the situation?

Click to expand...

Did you check that the brass pilot jet is actually in there?

As I've heard of instances before where new Amals had no pilot jet in them! But it does sound as if the fuel side of the pilot system could be blocked.

From what I've heard, I'd treat new Amals exactly the way I'd treat an old set of amals - go through everything just as if you had pulled it off a bike that had been sitting for years and had been badly wrenched by the PO. Check/clean all the passages and check/true all the mating surfaces on the carb and the manifold. Check the float level. As you know, there have been several different "recommended" float levels over the years. I have found that on my 850 with the original plastic floats, the .080 setting below the top of the bowl works best. I have tried the other settings but that's the one that MY engine likes the best.

And a request - If you do disassemble the carbs it would be very interesting if you would check for mating surface trueness and let us know what you find.

If you take the carbs off, take off the bowls, remove the pilot screws and shoot some carb cleaner with a thin tube into the adjustment hole. Check both carbs and see that the same flow is coming out of the top and bottom of the idle circuit for both carbs. I was having trouble with mine too, and I removed the floats yesterday because it seemed one of them was not stopping the flow of fuel through the needle valve, and I discovered I may not have had the pin that holds the float in place seated and the float was just loose in the bowl. It sure didn't run bad though. I could have knocked it off taking it off though. 1 1/2 turn has always worked good for me. Make sure your slides are synchronized at the top like JBA says.

The riders handbook for both the 68 and 69/70 lists 220 main jet and 107 needle jet. My 69 has 240 main and 106 needle. That is the way I got it and it seems/seemed to run fine so I didn't change it. Probably the PO changed them.

I originally set up my floats with the 0.08" below the bowl top and I could not get any tickle action, so I went back to just below the top like it was with the old plastic floats and so far so good. I may try back with 0.08 below again just to make sure.

I'm making up a rig to test the needle valves/float height today to make sure they don't leak.

Dave
69S

With all else checked and corrected as necessary, it's easy to check for air leaks.
With the bike outside away from any source of combustion, take yourself a propane torch, turn it on but don't ignite it.
Play the mixture over any of the mating surfaces while the bike is running and observe for changes in the idle speed. Act accordingly.
The advantage here is no mess from liquid sprays.

maximini said:

I just installed new Amal 930's on my 68. I've had the bike for a while but am just now getting around to getting it running. The right side carb does not seem to respond to the idle adjustment screw properly. The idle adjustment screw seems to need to be screwed way in to have any effect on the idle and the bike is not running right. I did the initial set-up the way I always have: 1-1/2 turns out on the air/mixture screws, 220 main jets, needle on the middle grooves, and everything sync'd per Bushmann's tips. The cylinder is definitely getting fuel and I did not find an obvious air leak.

Anyone have any ideas on where I should start to troubleshoot the situation?

Click to expand...

I have a similar situation with mine. One is adjusted correctly, but the other requires the idle screw all the way in. I've probed the pilot jet with a wire to ensure it isn't blocked and blown it free with compressed air. Lapped all the mating surfaces, etc.

I did manage to find an air leak where the flange meets the cylinder by spraying carb cleaner on the surface while the bike is at idle (an air leak here will cause the bike to stumble). Carbs are coming off next week to install some chromed brass slides, and when I reinstall I plan on using some high temp silicon to dress up the flange mating surface.

Cheers,

- HJ

I had some time last night to remove the offending carb and take a close look at it. The first thing I found when removing the was some staining on the cylinder side of the slide. When the carb was off the machine I removed the float bowl and discovered that the pin that the float pivots on was not fully into it's recess on one side. Under magnification it became clear that the recess was not as deep as the other side and that the rod was sitting on an angle. It seems as if the angle of the rod was just enough to cause the needle valve to wedge in the seat. I milled the recess a bit deeper (what a PITA) and cleaned the bowl out and glassed it to make sure it was flat.

The pilot circuit was clean as a whistle but I flushed it and blew it out anyway.

I also pulled the carb off the intake and noticed some staining/fuel on the outside of the o-ring seal which seems to indicate some air leakage. I pulled the o-ring and checked the flange and the intake for flatness. It seemed fine, but as long as I had the carb off the bike I decided to remove the studs from the intake and lap both surfaces flat. I chucked the o-ring and replaced it with a new one.

I re-installed the carb, but did not have any time to do the initial set up or re-install the tank, so I will have to wait and wonder if I have found the problem or not.

If that doesn't fix it, check the float height. I bought new float bowls (with the drains ) for my '70 w/ 930s and had a miserable time getting the pilot circuit to adjust and the engine to idle right. The needle seat on the new bowls was too high and the fuel level was too low.

Greg

This one could have you running around in circles, heres my story with brand new Amal bodies

One carb would not function at idle.

Eventually whilst squirting carb cleaner into the pilot circuit, via the adjuster hole with a tube on the spray can nozzle, I noticed carb cleaner venting through the plug inside the float bowl. This plug covers the mixing chamber were the pilot jet lives. I guessed that if fluid could leak through, air could suck in also, and probably collapse the vacuum inside the mixing area. And yes after simply smearing Devcon over the little plug and letting it set, the carb was pefect and the bike idled and responded to mixture adjustments.

Good preventative tip for anyone with Amals, whilst you have them stripped down.

HTH helps

Richard

I managed to get some time today to do the initial set-up on the carbs. I set them up per Bushmann's advice. The bike started right up and will idle all day at 800-1000 RPM. Both carbs now respond to the idle stop screws and the pilot adjustment. I can't find any air leaks.

When you rev the bike off idle it gets a little ragged. Ug-ug -ug-ug. I noticed that there was a pretty good amount of fuel mist vapor coming out the velocity stack side of the right carb when you rev the engine - no fuel vapor mist on the left carb though. Any ideas??