Honda Shadow Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
406 Posts
Discussion Starter · #1 ·
Hopefully someone can help me out with this. Whenever the bike sits at idle for a while the engine will start to slowly creep up from 1000 (where I set it) to about 1500-1700 rpm. This is just sitting there, no throttle, no choke, no nothing, in gear with the clutch in or in neutral with the clutch out. My plugs look fine, and the engine is warm. In fact I think it happens more often when it is warm. I can snap the throttle and bring the RPMs back down, but after a little bit they'll climb up again. I can do it twice at a light. What's going on?
 

·
Registered
Joined
·
61 Posts
Just a guess here as I have no idea how your carbs work but I've seen the spring on the jug get week and lett the air push it up increasing idle or maybe you have a slight vacumm leak somewhere letting it suck more air just my 2 cents and I've been known to get change back :lol:
 

·
Registered
Joined
·
57 Posts
I know if that happened to me, I'd first check the play in the throttle cable to see if it was was within specs. Start the bike and once at idle turn the handle bars to the full right, and then the full left, then to dead center just to see if the speed of the engine changes any. Don't know if that will help a lot, but I always look at the real easy stuff first. Ride safe.
 

·
Registered
Joined
·
4,689 Posts
I suspect a leaky carb diaphram. The most vacum that is pulled is at idle, and the diaphram pulls against a spring raming the needle down into the mid-range jet orifice. If the diaphram leaked a little the spring would be able to overcome the vacuum forces and slow let the needle rise.

That's my theory and I am sticking to it.....
....although I guess the other alternative would be a fuel bowl float valve not seating/sealing and allowing the fuel levels a bowl to slowly rise above the optimum level.....

Ok one of those too, someone with a little more experience might chime in soon.
 

·
Registered
Joined
·
3,761 Posts
Everyone is on the right track...

Everything they mentioned will cause the problem in question.

Air leak will definately do it and so will a faulty slide diaphragm.

But what a better way to go ahead and check everything out.
I don't suspect the cables would cause this particular problem,
but it's a good chance to check them and lube them.
Pull the switch assembly off and take a look at the cables.

To look for a vacuum leak (carb boots, etc)... Get a propane torch,
like a Bernzene or something similar. Turn it on and do not light it.
Hold the tip of it around the carbs, near the boots and anywhere there
is a hose... If the idle increases, you have a leak somewhere.

If you get nothing there, then I'd dig in to the carbs and check on the diaphragms .

The ignition control module CAN cause this too, but it's VERY rare that this happens.
The ICM controls timing advance and if it's going flakey and allowing
the timing to advance at idle, it will do exactly that.
I would look at that as the very last resort as it's very rare the ICM's
will do this.
 

·
Registered
Joined
·
406 Posts
Discussion Starter · #6 ·
My cables are lubed and not pulling, so I'm going to try what litnin described with the torch. I'll give it a shot and report back in a few days if I manage not to blow myself sky high.
 

·
Registered
Joined
·
5,238 Posts
Don't worry about blowing yourself up. Propane is only flammable in precise proportions, and you won't have those proportions, so it's relatively safe. What you are doing is adding fuel to any air that may be getting sucked in, so the engine will perceive this as a richer mixture and the idle will go up proportionally. As far as the engine is concerned, it's like you've pulled the choke lever a little. It's a good method for finding leaks, and it works well. Just be sure to really put the torch head as close to the engine as you can to get the highest concentration of propane that you can.

On some torch heads, the air induction holes are accessible. These are the holes that the combustion air is drawn into for the torch. Wrap a little electrical tape around these holes, and that will assure that the torch is putting out 100% propane, rather than pre-diluting it. This will boost the concentration for your testing.

--Justin
 

·
Registered
Joined
·
3,761 Posts
tubes_rock said:
Don't worry about blowing yourself up. Propane is only flammable in precise proportions, and you won't have those proportions, so it's relatively safe. What you are doing is adding fuel to any air that may be getting sucked in, so the engine will perceive this as a richer mixture and the idle will go up proportionally. As far as the engine is concerned, it's like you've pulled the choke lever a little. It's a good method for finding leaks, and it works well. Just be sure to really put the torch head as close to the engine as you can to get the highest concentration of propane that you can.

On some torch heads, the air induction holes are accessible. These are the holes that the combustion air is drawn into for the torch. Wrap a little electrical tape around these holes, and that will assure that the torch is putting out 100% propane, rather than pre-diluting it. This will boost the concentration for your testing.

--Justin
... and to add one thing that I should have tagged with...

Do this in a well ventilated area.
Like tubes said, with one of the small torches, you wouldn't have enough
quanitiy to get the air/fuel close enough to ignite, but you don't want
to be breathing that stuff in a closed environment.

Always play it safe.
 

·
Registered
Joined
·
1,300 Posts
litnin said:
Everyone is on the right track...

Everything they mentioned will cause the problem in question.

Air leak will definately do it and so will a faulty slide diaphragm.

But what a better way to go ahead and check everything out.
I don't suspect the cables would cause this particular problem,
but it's a good chance to check them and lube them.
Pull the switch assembly off and take a look at the cables.

To look for a vacuum leak (carb boots, etc)... Get a propane torch,
like a Bernzene or something similar. Turn it on and do not light it.
Hold the tip of it around the carbs, near the boots and anywhere there
is a hose... If the idle increases, you have a leak somewhere.

If you get nothing there, then I'd dig in to the carbs and check on the diaphragms .

The ignition control module CAN cause this too, but it's VERY rare that this happens.
The ICM controls timing advance and if it's going flakey and allowing
the timing to advance at idle, it will do exactly that.
I would look at that as the very last resort as it's very rare the ICM's
will do this.
Litnin, I think I read somewhere that you can use WD 40 spray rather than propane and get the same results.
Any comments?
 

·
Registered
Joined
·
336 Posts
Yeah, WD-40 or carb spray cleaner will work. These can both be a little rough on the rubber parts though.

The main thing is safety, the WD-40 and carb cleaner are both highly flamable, and so is the propane. The difference is, the propane, if it ignites, will just flash quickly, the WD-40 and carb cleaner are will burn until all the liquid is gone, can get the whole bike torched if there's enough liquid everywhere.

Gumpy
 

·
Registered
Joined
·
406 Posts
Discussion Starter · #12 ·
I got out the torch and managed not to burn anything down or lose any facial hair. I didn't manage to find a leak either. When I stuck the torch right in the intake I only noticed a light rpm rise, maybe 50 or so. It was noticeable, but not incredible. Then I tried out all the areas that I thought there could be leaks coming from but couldn't see or hear the motor running harder in any spot.

I wasn't satisfied, so I took off the airbox and had a look at the carbs. I played with the needle slides and they seemed like they might possibly be catching slightly about halfway to being fully backed out. That got me thinking that maybe my problem was with the diaphragms, but I'm still not convinced because my top speed is over 105mph. Could this be something that will cause a problem later?

I went to put the airbox back on to call it a night, and noticed something funny. The rubber on the right hand side had some kind of sticky goo holding it to the plastic, but the left side didn't. The way it is set up, there's a very small area for a seal to be formed on for that left rubber, and it was loose enough to turn it easily.

Hmmm... I thought... it's when the wind is coming from the left that I have the worst problems.

I'm pretty confident that I found my air leak here. The only stuff I had laying around was some RTV silicone gasket maker, so I gooped a bunch on and I'm hoping it will stick to both surfaces and make me a seal. I'll let everyone know if the mystery has been solved.
 

·
Registered
Joined
·
406 Posts
Discussion Starter · #13 ·
OK, I really need some help with this. I went for a ride today and my bike ran like crap. I get back and I'm so frustrated that I tear into it right away. I found gas on the ceiling of the air box! After scratching my head for a little bit I started the bike up and noticed that when I got on the throttle gas would spatter all over the place up to three feet in the air. Not in huge amounts, but I could see little droplets flying out. I know that isn't right.

My idle has been going wild because gas gets all over the inside of the carb throat and starts sliding down towards the cylinder. Once it seeps past the blade and hit the cylinder head it evaporates and speed the idle up.

I took my diaphragms out and they were fine and I just cleaned my jets before the winter, so what the h3ll is going on with my bike?
 

·
Registered
Joined
·
90 Posts
Hate to resurrect an old thred but did a search and found this. I was hoping there was a resolution. My bike is doing the same exact thing. Slide diaphrams are good, carbs rebuilt, rtv silicone on the air intake assembly, no detectable vacuum leaks . I am currently re syncing the carbs and messing with the pilot screws. Currently 3 turns out. I did do the hole saw mod to my exhaust but did this prior I believe. Let me know your thoughts.

Thanks
 

·
Registered
Joined
·
90 Posts
I hate it when I search for info and find like issues and as I read on, dead end. No resolutions. I have found many. Too many.

Anyway with no response, I just carried on with my troubleshooting and going with what I could find here.

My bike ran ok when I got it but no power. Cleaned carbs and found slide diaphrams were shot. Posted thread about that issue. Anyway I did the hole saw mod after that and left the baffle but went thru to the header. I like the sound but it screwed up my carburetor settings. I did a sync but I did find I had my pilot jets out 4.5 turns. Not 3 as I said earlier. Even at that it ran terrible. I think the idle increase was due to overspray of gas on the top of the air snorkle.

Anyway, today I put in #45 slow jets replacing the #40's I had and now my pilot jets are out 3 turns. Bike runs great finally again and I am all grins. I like the exhaust mod as well now that the bike is running good. I thought I ruined my bike for a while there.

Tomorrow will be a day of just ridding. And grinning.

Anyway I just wanted to close with a resolution for others.
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top