Choke will not increase RPMs

[pinetum]

I have a strange problem with the choke on my '83 VR. I had to add throttle when I tried to start it and then discovered that the choke did not increase RPMs as it normally does. The choke part seemed to work as it stalled the engine when I applied full choke. No matter what position I tried the choke the RPMs though never changed. I checked all the linkages and all seemed to be operating properly. I had rebuilt the bike several years ago (with much VR.ORG help) so am familiar with most operations. Perhaps I don't know exactly how the enrichment system works? Does the choke move the throttle to increase RPMs or is the enrichment function supposed to increase RPMs? If I apply the choke and move the throttle slightly, I can get it started. It ran just a few days earlier but seemed to have a problem getting up to speed. Don't know if these are related problems or not. I checked all the links that referred to choke problems but did not find any that related to my specific situation.

Any suggestions would be appreciated.

 

Pinetum

[MiCarl]

First off, it isn't exactly a choke. A choke restricts air flow to make the fuel mix richer. Motorcycles with true chokes often have a linkage to open the throttle a bit when the choke is on.

 

What your carburetors have are enrichment circuits. They're quite a bit like a parallel carburetor except with a rich fuel mixture. When you open their throttles (by moving the "choke" lever) that rich mixture is added to whatever the main carburetor is doing. That rich mixture helps it start cold and the extra fuel/air makes the engine run faster.

 

The enrichment circuits can compensate for dirty jets or air leaks affecting the idle circuit, but they are limited on how much they can do.

 

Also, the enrichment circuits have their own jets and can get gunked up just like the regular jets.

[cowpuc]

If it were mine I would start out by spit check the headers to make sure it's running on 4.. What your describing could be related to having a fouled plug. These scoots have the smaller plugs in em which dont take kindly to being blackened from a little over chocking and its amazing how well they will run on 3 cylinders - except for little things like you are describing..

Would type more suggestions but I gotta run to the Doctor,, will check back later and see how ya come out..

[camos]

When you open their throttles (by moving the "choke" lever) that rich mixture is added to whatever the main carburetor is doing. That rich mixture helps it start cold and the extra fuel/air makes the engine run faster.

 

The enrichment circuits can compensate for dirty jets or air leaks affecting the idle circuit, but they are limited on how much they can do.

 

Also, the enrichment circuits have their own jets and can get gunked up just like the regular jets.

As mentioned the enrichment circuit can get jammed up just like a carb does when a bike is not being run on a regular basis. Running with Seafoam in the fuel will help clean gunky carbs and it will also help open up the enricher circuit. When treating an engine with Seafoam it is a good idea to also open the choke so it can work its magic on that circuit. So don't use the choke just to start the engine but leave it open for an extended time to allow the treated fuel to run through it. As when using a treatment to clean out the carbs, it can take a while to be effective so it can also take a while to also clean out the enrichment circuit.

[pinetum]

If it were mine I would start out by spit check the headers to make sure it's running on 4.. What your describing could be related to having a fouled plug. These scoots have the smaller plugs in em which dont take kindly to being blackened from a little over chocking and its amazing how well they will run on 3 cylinders - except for little things like you are describing..

Would type more suggestions but I gotta run to the Doctor,, will check back later and see how ya come out..

 

 

Plugs were just replaced last fall but took them out anyway and did find the 2 rear cylinders (#1 & #3 ) with some carbon on them. Cleaned all the plugs and checked fire and plug resistance. All was good. Got bike started and then realized the #4 carb diaphragm/piston was not moving. Took it apart and piston had separated from sleeve. Fit was very loose but could not find any problems. Probably need to replace the piston and sleeve. Diaphragm was good. Any suggestions where to get these parts at a reasonable price? I don't know if this caused the starting problem but don't think so. It probably caused the poor power-up though because these activate at higher RPMs.

 

Thanks for your help.

 

Frank P