Rear carb sucking way more air than the front carb

[sevenmilebridge]

OK had to put new nozzles and needles in the carbs on a 2000. Had throtle bodies rebuilt no leaks. For some reason the rear carb is drawing way more air than the front????? With the old nozzles and needles had them very close but couldn't get idle speed lower than1200 rpm with the idle nuts closed all the way. Any ideas........

[redroadster]

Check the throttle plate adj.
and for vacuum leaks at the head
Take 1st pump compression test never hurts too

[nismou20]

I always take the domes/pistons off so you get an idea where the butterfly valves are in relation to each other first. That will get you in the ballpark for syncing. Then proceed on to adjustments.

[23yrRebuild]

Make sure the domes and pistons are matched correctly...try reversing them to see what happens, and don't forget the damper fluid.

[keith0alan]

Check the wiki section for carb adjustment instructions.

[sevenmilebridge]

OK the engine has been rebuilt its brand new. I put in new nozzles because I couldn't get the engine to idle below 1000 rpm. With the old nozzles had the carbs balanced pretty good no stumble drove well. New nozzles the rear carb is pulling major air. Can put my fingers over rear carb and they get sucked in over the front carbs no noticeable difference. Used carb cleaner to test for leaks no leaks. Can not get it to idle smooth at all I'm about ready to put the old nozzles back in.

[spl310]

Have you balanced the carburetors? You seem focused on the jets, but the issue with one carb pulling more than the other is a balance issue.

[redroadster]

What happens pulling #1 & #2 plug wires running ( cyl balance test )then 3 &4 is compression in 1 pump the same , possible head gasket blown between 1 &2
With air cleaner on doing the same ?
Not a carbon track in dist cap , that can cause a symtom like this , fuel new ? plugs poss. Fowled somewhat , excessive carbon build up on intake valves. Should have cleaned off

[sevenmilebridge]

Put in an electronic ignition new valves pistons bearings timing gears and chains new valve springs cylinders bored crank turned cant get the carbs to balance. Had to walk away from it today try again tomorrow

[keith0alan]

Air flow balance has nothing to do with jets. Sort the air flow balance. there are several possible causes all involving the linkages.

[redroadster]

Sounds as if it's running only on the back carb via the cross over / balance pipe , assuming its that setup , the lack of power can equate to reduced air flow ( this is why I instructed to do a quick compression test. That confirms if it's equal.) put a bal bearing to stop fuel flow to the back carb then try it or call the person who rebuilt them , HF s vacuum gun pushes pressure to good to test such

[Gregs672000]

I am not fully familiar with all the different carb linkages, but here's what I would do... as Keith said... take a breath and look at how the carb linkage works and what does what to open the throttle plates because unless there's a major intake leak (which I doubt and you have checked for) it must be drawing air past the throttle plates. You should be able to pop the dog bones off to isolate/separate the carbs from the linkage. There's probably separate screw type adjusters that directly open or close the throttle plate on each carb. Confirm that you can adjust them so both throttle plates can be set the same independent of the linkage. Then, look at the dog bone connectors and note what happens to each throttle plate when you attach the dog bones... you may find one is shorter than the other and opens the plate more or vise versa (too long). If thats the case, then you need to adjust the length of the dog bones until they are the same and DO NOT CHANGE THE POSITION OF THE THROTTLE PLATES WHEN YOU SNAP THEM BACK ON... they are just there to make a connection. Some dog bones are not adjustable... post if yours are not. Then there should be a balance adjustment screw that operates on a tab on the linkage that connects the two carbs via the linkage. Adjust that screw and note what it does to change the throttle plate position via the linkage. Sometimes there is one carb that is like "the master" that you then use the balance screw to adjust the opening of the other carb's plate (more open or more closed) to "balance" to and thusly flow the same air. Based on your earlier posts, I'm betting that you had some linkage issues prior to your carb rebuild... it is extremely important to understand how the linkage works and what adjustments do to change the throttle plates. If needed, take a look at the manual and compare your linkage to the pictures. I also suggest you post a pic of your linkage so we can see what's what and many be able to point out something you're missing. Don't worry, we'll get it!

What you want is for the individual throttle plate screws to set minimum throttle plate opening on each carb (sets idle), be able to attach the dog bones without changing either throttle plate opening when tied to the linkage, and to be able to use the balance screw to fine tune the linkage so it opens the throttle plates equally at idle and throughout the sweep of the plates via your foot.

Hope this helps!

[sevenmilebridge]

I would like to thank everyone that responded to my problem. It turned out to be a slightly bent tab that is below the idle screw so even backed off all the way the throttle still was open just a bit. I was able to fix and big relief thanks again.

[Gregs672000]

Yeah! Glad to hear... sometimes stuff happens eh?