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Bad throttle response when the engine is hot???

Jethro

Jethro

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It seems that when my bikes motor gets hot, the idle speed increases and the throttle response down at the low rpm's gets crappy. When cold, after I get it started, it has great throttle response and idle.

The bike is an 831100e with 4 into 1 pipe, K&N stage 3 jet kit with pod filters.

Another possible symptom is that when I start the bike while stone cold, it's real hard to start. Nothing new for our old bikes, but here is what I have to do to start it. Full choke and it starts right up and then stalls immediately. Then I use half choke and crank, crank, crank, crank, crank until it finally bobbles to idle and I immediately go to no choke. It then idles like a champ. At this point, if I use any choke, the bike stalls. When the engine gets hot, if I use the choke, the engine rpm's speed way up.

Does anyone have some feedback on this problem? I have yet to mess with the carbs since I got the bike because it is pretty drivable as is, but I want it to run perfect. Thinking about ditching the D&D exhaust and pod filters, and jetting back to stock.
 
Sounds like intake leak(s) to me. Manifolds or the o-rings if you have them.
How much is the idle increase once hot?
 
Probably only 3-400 rpms, but what really makes the difference is the throttle response. When it's cold, if I blip the throttle, it's instant rpms. After it's warm, when I blip, it stutters a half second then gets going good. I'm contemplating not doing anything about it because the drivability above 2000 rpms is perfect, but if I can do something about it, I would.

A little more info, I did a plug read after some general around town riding and the plugs were all pretty much perfect. Maybe a little dark, but a mocha color, not black. And all of them were exactly the same color.

I'm gonna do a carb synch tonight, and I'll check for leaks. When you say o-rings, what exactly are you talking about? I was going to check the carb boots, but I have pod filters, so there aren't any airbox leaks to check for. I'm not sure of any other places to check for air leaks. I have CV carbs- it's an 83 1100.

Thanks Kieth- you've helped me with my 81 1100 before!
 
Some models have o-rings in the manifolds. 3-400 rpm gain is not bad though. No more than that though. My bike picks up about 2-300 rpm after warming up.
I gotta leave for work but if I think of something I'll let you know. The carb synch you mentioned is ALWAYS a good idea. :)
 
Hi. I gave your problem some thought but I can't come to a conclusion.
I'm getting mixed signals regarding how your choke effects the engine. Generally, choking a hot engine will kill or make the engine stutter a lot. If choking your hot engine actually increases the rpm's, then it would seem you're running lean or have an intake leak. But I would think the intake leak would have to significantly increase your hot rpm's too. Your minor increase in rpm's once hot, doesn't suggest a leak. But if choking the hot engine does increase the rpm's, I have to say you're running lean. However, your plug reads say the mixture is fine.
Then you say choking the cold, running engine (after it has started once and then stalled) will kill it. When the engine is still cold, the choke shouldn't kill the engine, the rpm's should increase. So your problem would suggest the bike is running too rich when cold, so adding choke further richens the mixture and the engine stalls. Like I said, mixed signals. Or you may have more than one problem.
It doesn't seem out of synch carbs would cause your problem, but you never know. We all know how important balanced carbs are. Your even plug reads suggest the carbs are reasonably balanced too.
On our older bikes, throttle response does change a little from cold to hot.
My bike runs good, but I get just a little less crisp throttle response when the engine is hot too. My carbs are different than yours though. Have you compared your bike to others? Maybe it's not really a problem. Your pods/pipe can cause "driveability" issues. I'm assuming the jetting was done right. Part of re-jetting the CV carbs is to drill out the vacuum orifice to the pistons (slides). This is a requirement to improve throttle response. If yours were not drilled out, I would think this would effect BOTH hot and cold throttle response though, not just hot throttle response.
I would go ahead and do the carb synch and check for intake leaks. Can you tell if all the choke plungers are operating smoothly and raising/lowering the same amount?
Did you inherit this problem, or did the bike just start doing it?
 
lag

lag

put a new set of plugs in it, if you have been tuning it or getting the motor overly rich on start up you may have saturated the center insulater, my 1000 ran great cold the when warmed up was hard to get off the line I used the plugs for tuning the carbs a bunch of times and even though they were not fouled looking they showed signs of shorting down inside the insulator, new plugs cured it till I contined to try tuning the carbs, then I got pissed and dropped my mufflers and used my exhaust analyzer to get them set up right, man the 1000 made my ears ring with out the muffs
 
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