Run with choke, dies withthrottle

Total noob so please excuse the my cluelessness.

Tow bikes, daily rider and parts bike (trans shot).

Carbs on daily rider need rebuilt. Bike does not start in the cold and does not idle well until warm.

Parts bike starts and idles well. Only rides in 1st gear which is mostly useless.

Moved carbs from parts bike to daily rider. I plan to rebuild the daily rider carbs during the winter. The hats on the parts bike carbs are horribly rusty.

I want to ride the daily rider while I am rebuilding the dailt rider's carbs.

The daily rider bike now starts easily with choke on. When I try to give throttle the engine dies. When I advance the choke the engine revs higher and when I decrease the choke the engine slows.

The throttle cable seems a tad slack but the throttle cable does pull the proper lever on the carbs.

I have yet to re-attach the airbox rubbers properly. Could the lack of airbox/filter resistance cause the problem?

Any idea?

 

Each carb should be considered custom set up for the bike it was on. Simply switching a running bike's carb to a bike that may have carb trouble does not mean the job is over. You will need to tune and sync the carbs to the bike. I just did a swap to verify the new bike's trouble was indeed carb related. After completely disassembly and cleaning of the bad carb, I returned it to the bike it came off of.

 

Take the bowls off the parts bike carbs, put them on the daily rider carbs, and reinstall them on the daily rider bike. The carbs should now start cold, and idle fine assuming the bike ran when warmed up.

 

Thank you Gamuru. That makes sense.
I will give that a try.

Do I need new bowl gaskets to put the carbs back together?

 

If you're careful that you don't rip them, no.

 

Ok, I will give it a go.

Questions.

1. When separating the bowls from the uppers, will parts fall out? Should the hats face down or up when disassembling?
2. If I take the bowls off of the bad starting but good running carbs, can I just clean the enrichment well to make it start and idle properly?

 

1a. Nope. 1b. It shouldn't matter.
2. You can. In then, if you're planning on rebuilding them, you'll need to. Now or later. It's up to you.

 

I will let you know how it turns out.

Thanks

 

I'm glad you made sense of that, 'cause I'm baffled by it... and I wrote it. :?

 

The Carbs aren't going to be running right until the Airbox Boots are fitted and there are no air leaks.
That the Bike would run with the Choke on does not surprise me; because the Carbs ARE running too lean without being limited by the shared and limited flow of the Airbox Intake.

Once you hook-up the airbox and get all the leak-points tightened-up; try running the Bike without so much Enrichment.

This, of course, follows the Carbs being thoroughly cleaned and prepped for tuning.

 

Rick

I will tighten up all the airbox boots and put the air filter in to see if it revs without dying.

I am not trying to short cut, but I thought that if I could kludge together a working arrangement for occasional riding I could enjoy riding the bike to work as I rebuild one set of carbs.

One reason I bought a parts bike is so that I could choose what parts could be used right away and what needs to be restored and/or replaced.

I plan to do the proper tuning once I get one set of carbs rebuilt.

Thanks for the advice.

 

The Carbs need the restricted and shared flow from the Airbox. They run too lean without being hooked-up right.
This don't mean you hook-up the airbox and its going to all hunkie-doorie.

Carb problems don't generally iron themselves out.
If theres gook and gum in the bottom end ... it won't matter what you do until its cleaned-out of there.

 

Point(s) taken.

The boots are all bottoned up now. I put a new air filter in the box and buttoned it up.

Tomorrow I will start it and see how it goes.

Thanks for the help. I look forward to cleaning and restoring one set of carbs per your write-up in the FAQ.

 

Here is the update.

Installed air filter. Buttoned up the airbox and airbox boots.

Bike idles with choke but dies with throttle applied.

So, its starved for gas and there are no visible air leaks. All the boots look to be in good shape with no visible cracks. I am thinking maybe the make-shift IV bottle hanging from a coat hanger is not working properly. I raised the bottle and got all the air bubbles out and the bottle is now almost empty. So, I open the bottle and re-fill with gas, about 6-8 ounces. Put the bottle back together and re-hang it. Get the bubbles out and ,VOILA, it now starts, idles and REVS !!!!!

So, lesson learned. It takes XX ounces (8-10?) of gas to fill up a set of 4 carbs enough for the throttle to work.

I suspect that the enrichment circuit gets the gas from the bottom of the carb bowl but the throttle requires the bowls to be full and thats why the choke worked but the throttle did not.

Is that correct?

It would be nice if there was a window into to the carbs so that you could see what is happening inside.

I will now put a tank back on and the seat and go for a spin around the neighborhood. It may have to wait a couple of days as we are in for some rain tonight and tomorrow.

Man its nice to twist the trottle and get that high-rev growl.

 

Sounds like you've got it figured out.

Yes, the enrichment pulls from the bottom of the bowls.

 

I love this XJ forum.
The pictures and write-ups are awesome.

I got the idea to use the el-cheapo squeeze bottle from the sticky thread about what tank to use for tuning.

Thanks guys.