Author Topic: Idle speed doesn't change  (Read 2299 times)

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forthekids

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Idle speed doesn't change
« on: February 20, 2019, 08:58:52 AM »
Hey Everyone,  I have a 1978 Invader 440.  I just changed the crank seals, cleaned carbs, recleaned carbs, repaced o-ring at bottom of carb, checked for air leaks with carb cleaner while running, replaced all fuel lines, put new inline filter in fuel line, and made sure airbox is clean.  I have two problems, first I am unable to get the sled to idle over 2000 rpms.  Its supposed to be 3000.  When I first start the sled it will idle at 4000, but soon after starting (1 minute or so) the rpms drop to 2000 and nothing I do will keep them above this.  second question is that it does have bog when I first hit throttle.  If I use the throttle to hold rpms around 3500 for a second or two before actually trying to go it really rips?  Any tips on things to look at.  The needle clip is in the middle position.  It actually ran way better before doing the crank seals, however they did need to be replaced as they were forsure bad.  last person to install them had only done mag side and you could see they didn't take the case apart bacause the sealing rib on the O.D. of the seal was smashed and tore off when jambed in.  Thanks in adance for any help.

gixxer6

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Re: Idle speed doesn't change
« Reply #1 on: February 20, 2019, 01:36:28 PM »
It sounds to me like it may be running too rich on the idle.  Where is your idle air screw set?  Have you checked the choke cable adjustment?  Did you inspect the rubber seals on the bottom of the choke plungers? 

forthekids

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Re: Idle speed doesn't change
« Reply #2 on: February 20, 2019, 02:19:36 PM »
I made sure that the choke cables have slack in them when the choke is released.  I looked at the rubber on the bottom of the plunger, it looked OK, but I didn't do anything further then that.  I started with my air screw at 1-3/4 turns out from full seat on both carbs and the idle screw  3 turns out from coil bound on each.  This got it started fine, but in an effort for higher Idle RPM I have tried turning my air screw in to only 1 turn out from seated on each carb and turning the idle screw out 1-1/2 from coil bound.  This doesn't seem to do anything.  I read about others turning the air screw in to only 1/4 turn out, but I hate to risk wrecking anything by leaning it to far out. What are your thoughts!  Thanks 

mswyka

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Re: Idle speed doesn't change
« Reply #3 on: February 20, 2019, 04:25:15 PM »
I had an Invader that worked fine when it first came home on the trailer after putting some used jets into the carburetor.  Then we rebuilt it with all new parts.  After the rebuild, it refused to idle and it was necessary to milk the throttle to get the sled moving.  Once it was moving it ran great.  I gave up and sold the sled.  The next owner popped in some different carbs and it ran fine.  About the only thing I can figure was that we had a bad pilot jet(s) or somehow, even with  all of our  cleaning, we did not get one or the other pilot fuel passage clean.

So hearing what you are saying, if it runs correctly above idle it might be worth double checking the pilot circuit.
Intruders:  1978, 1979, 1981 Custom (Pink)
Invaders:   1980 440
Projects:    1981 Invader 440

gixxer6

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Re: Idle speed doesn't change
« Reply #4 on: February 21, 2019, 07:07:02 AM »
I agree with Mark, you have a problem with your pilot circuit.  If the carbs were dirty the jets should be replaced.  Once there is gunk built up in the jets it is nearly impossible to get it out properly.  And definitely not worth the hassle over the few dollars it costs for new jets... 

forthekids

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Re: Idle speed doesn't change
« Reply #5 on: February 21, 2019, 12:38:50 PM »
I have new main and pilot jets ordered and on the way.  I will update with results once installed.  Thanks

gixxer6

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Re: Idle speed doesn't change
« Reply #6 on: February 21, 2019, 01:11:25 PM »
That's a good start.  If you're not familiar with these carbs google "Mikuni VM carb diagram" and make sure you can spray carb cleaner through all of the pilot passages.  I use a can of carb cleaner and the little red straw, that seems to work quite well.  Good luck! 

forthekids

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Re: Idle speed doesn't change
« Reply #7 on: February 26, 2019, 07:22:15 AM »
I changed the main and pilot jets with new ones.  I use the stock sizes listed in the book.  The pilot jet read that they were the same size but the new one's holes were much smaller. I'm not sure why that was however I also noticed that it was getting little to no spark on the right cylinder.  I changed the plug and also cut 3/8" off the spark plug wire and re threaded the end back on...it doesn't idle any better really, still only sits at 2,000 rpm's however she really rips now.  Way, more snap and top end power then I ever remember.  Thanks guys

mswyka

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Re: Idle speed doesn't change
« Reply #8 on: February 26, 2019, 05:06:24 PM »
The main jet/needle jet has a moat at the top.  This often gets clogged with gunk.  I have attached the best photo that I have.  It is a very small moat and there is a pilot air passage that comes into this section of the needle jet to atomize the fuel.  Be sure to clean that area thoroughly.  You will probably need to pull the needle jet out of the carb to do this cleaning.
Intruders:  1978, 1979, 1981 Custom (Pink)
Invaders:   1980 440
Projects:    1981 Invader 440