choke kills

my bike runs awesome once warm. starting cold however is another story. it will not stay running unless i apply throttle for a few minutes to warm up the engine. When cold, if I engage the choke at all, the bike dies. What is the problem and could some Sea foam fix this issue?

 

Heh, I have a 1985 XJ700 as well and that is just the nature of the beast, my friend.

The bike has to warm up a little and starting cold with the choke half way on or all the way on is normal.

Applying the choke actually opens up a valve that dumps extra fuel in front of the butterflies in the carb. When the bike dies it is because the extra fuel is flooding the cylinder heads and extinguishing the sparks. This means your choke is working correctly.

To fix the problem either start the bike with the choke off and after 10 seconds of keep the throttle a little open throw is wide open for about 10 more seconds. This usually warms up mine enough to keep the idle. Or just start with the choke on and ride down the block and then close the choke.

 

just curious about the "nature of the beast". would I be wrong to assume that 25 years ago if i bought a new Maxim off the lot, the bike would not start and run with the choke engaged? I have cleaned the carbs and adjusted the float levels. I have also cleaned the little passages in the bottoms of the float bowls and carb cleaner can now spray a few feet out after traveling through the passages.

I'd like to think that back when the bike was new it would have fired up cold with full choke. Did it?

 

The bike should indeed start with the choke on if it's cold. However, if the surround air is too warm then the bike will not start with the choke full on and it should start with the choke off.

If you want a bike that will start perfectly in all weather and not need a warm up period, buy something with fuel injection.

 

1985xj700

You could have an air leak, bad or fouled jets, etc.

My 1982 starts and idles like a dream in 15 deg weather.
It does require feathering the choke. Its easy to apply too much or too little.
As it warms I have to reduce the choke to get smooth idle.

I have zero problem starting in 0 deg wind chill.

Have you synchronized the carbs? My bike ran poorly until I synched the carbs.

 

Thanks HalfCentury

I have not syched the carbs. Could that be the culprtit?

As far as a possible air leak, my airbox and boots are all tight and in good shape, but that is a good idea for a possibility to pursue. It makes sense that when starting there would not be adequate vacuum to pull fuel until the engine got to running stronger if there was an air leak.
I have been through my carbs and cleaned all the accessible jets (main jet, pilot jet, little jet in bottom of float bowl. I did not break the carbs apart though.

 

If you haven't synced the carbs that could very well be it. Made a monster of a difference on my seca. I don't know if you have a YICS engine or not, but I do, and I didn't have a YICS-blocking tool, so I just didnt use one. It was rather ... challenging to get an accurate reading from the vacuum gauge. But after enough fiddling, it went fairly quickly. As you get closer to synced, smaller turns on the screws make huge differences in the smoothness of the engine. I got my vacuum gauge from ace hardware for about $7 as I recall, so I'd give it a shot. Theres a very well-written how-to on carb syncing (by rick i think?) on here. Walked me through it, and my only experience with carbs to that point really was removal and reinstallation of car carbs.

 

Unsynched carbs will cause all sorts of silly behavior especially at low-throttle/part throttle and idle. (If it will idle.) Dirty carbs however will cause the same symptoms. Ensure they're RELIGOUSLY clean; do the "clunk" test; then go thru the synch processes. Once the bike will actually idle you can check for air leaks with an unlit propane torch.

 

Heh, my bad 1985xj700. I thought you meant it was all running fine and had been tuned but just had a problem idling when it was cold.

Yeah, sync your carbs and make sure everything in there is nice and clean. Dirty emulsion tubes and clogged pilot jets can cause serious problems.

Also, like I just had an ordeal with, make sure your air filter is good and clean and in good shape. Never knew an air filter could cause so many problems.

 

I hate to resurrect an old thread, but the issue I am having with my 85 xj700 is almost identical.

It will start in cold weather and will idle just fine with the choke on, however, once it gets to about 45 degrees, it will start, and idle only if I give it some throttle otherwise it will die out. Even then it keeps the idle at about 600 - 700 RPM.
I have tried playing with the choke and having it on at about 1/3 open seems to help a little bit, but the idle is still ridiculously low and after about 30 seconds it will die out. The thing is, once warm (taken around the block a few times) the idle sits perfectly at 1000-1050 RPM.

As per my other posts, the carbs are completely clean, pass the clunk test, the enrichment circuit is clean, all carbs are synched and have been tuned (although not extensively). If I fiddle with the idle screw at start up, I can get the bike to idle at 1000 RPM, however, once warm the idle jumps to about 1500 which results in me having to fiddle with the idle screw again (not pleasant when the bike is warm).

Is this normal or am I missing something?