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Hoping somebody has some experience with this so that I can stop pulling my hair out!!



OK, I bought an 87 Interstate that had sat for 7 years. Initially it would not run due to that wonderfull stuff that old fuel turns in to. After the 1st round of carb cleaning it ran fairly well, but had a 'muffled' sounding backfire that you could tell was coming up the intakes. WhenI balanced the carbs, only cyclinder 2 intake vacuum would drop off during the backfire. The bike idles well once warm and the backfiring seems prevalent fromabout 1250 to 3000 rpms, after that it smooths out. On the road, you can tell the engine is holding back during this rpm range. The second round of carb cleaning really didn't find much, but they were soaked in cleaner and blown out with high pressure air again. Engine still has the backfire problem. I will be checking cyclinder compression this week after I borrow a gauge. During idle, I have checked the exhaust pipe temps at the headers and they all are within a few degrees of each other, so they all are firing well at idle at least.I still have to put newspark plugs in it, that will be done this week.



ANY help, questions, answers, or general chit-chat is always appreciated.



THANKS,...Chris.
 

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I performed the last carb cleaning this weekend and checked the float heights(I forgot to do this the 1st time), they all needed adjustment. I set them to 9/32 as stated in the manual.



I have afeeling that it might be a valve problem, but don't have the experience to know for sure. I'm hoping the compression check will tell me something...



THANKS,...Chris.
 

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Welcome to the forum! Had the same problem with my '84 Aspy. Sat for about 2 years and a multitude of carb problems. Check and double check float levels, make sure your float needle valves are in good working order. I found one of mine had the rubber tip separated from the valve body. Bought the OEM set for $138. Aftermarket needle valves are questionable:

http://www.randakks.com/TechTip60.htm

Also make sure the float pins are allowing the floats to pivot freely.

Spring for the $99 carb rebuild kit from Randakk.

http://www.randakks.com

It's the best there is and you get everything. I also removed and cleaned out my reed valves & chamber really well. They were filthy. After buttoning everything back up I had no more backfiring.

It sounds like you're on the right track and everything is clean, so not really necessary to consider using Seafoam in a couple tanks of gas. You still can and it won't harm anything.

Good luck!
 

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Mark,

Thanks for the input. I left a few things out of my initial post, I bought and installed 4 OEM carb rebuilt kits from the dealer. I have also run a tank of gas with Sea Foam. This afternoon during lunch break, I took it to get fueled up as the tank was pretty low(this was the gas with Sea Foam). I put premium fuel in her and took it for a drive. The bike seems to be running much better with a lot less backfiring, but it will still occasionaly.



You mentioned cleaning your reed valves and chamber. What are you referring to, where would they be?



THANKS,...Chris.
 

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Good....so you're ahead of me!

:clapper::clapper:

The reed valves/chamber is located on the underside of the intake plenum. You'll have to pull the carbs to get to it. It's dead center on the underside of the plenum.

When you bought the OEM rebuild kit did it include the air cutoff valve as well? If so, you're pretty much good to go.

How about the idler screws? Adjusted to specs? Tighten them until they gently seat, then back them out. I have mine backed out 3 complete turns.
 

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rcmatt007 wrote:
I think the reed vlaves were on the fuel injected model
Mine has the reed valves.
 

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Wrong Schematic....see #16 below... reed valves/chamber are not part of carb assembly.


 

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Thanks for all the info go out toeverybody. I have not looked at the reed chamber or air cutoff valve. Can anybody enlighten me as to what they do? Man, I just had the intake out of the bike 3 days ago, not looking forward to doing it all over again. Maybe the third time will be the charm. Over the next couple of days,I will work on it and take a look at the reed chamber. I also had the speedo quit working yesterday....



To answer some questions, the idler screws have all been set to the factory 2 1/8 turns out, and they were removed during cleaning.
 

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I did mine a total of 5 times before getting her correct. Next time /or next bike I will definetly rebuild from the jump and avoid the headaches associated with removing the carbs 5 times.

Check your float valves, the screens behind the float valves, make sure all jets are clean and you can see light through. Clean your choke valves.
 

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Complete the cyl compression of #2....backfiring back through the carb sounds like an intake valve leaking.. also check valve clearances, which could cause the same thing....
 

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I hate to say it but I would bet that carb needs to be cleaned better. From my experience coughing or sneezing thru the carb is a sign of a lean condition. You say it happens from 1250-3000rpms, that would indicate the low speed circuit on that carb is starving for fuel. It stops after 3k, if it was a bad valve it wouldn't get better. Your high speed jet is allowing the proper amount of gas in the cyl so it smooths out.Thats my 2cent stimulus opinion.,,
 

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Big Cahuna wrote:
I hate to say it but I would bet that carb needs to be cleaned better. From my experience coughing or sneezing thru the carb is a sign of a lean condition. You say it happens from 1250-3000rpms, that would indicate the low speed circuit on that carb is starving for fuel. It stops after 3k, if it was a bad valve it wouldn't get better. Your high speed jet is allowing the proper amount of gas in the cyl so it smooths out.Thats my 2cent stimulus opinion.,,


I would agree if it's coughing or a light popping sound it's a clogged low speed circuit.
If it is backing firing back though the carbthan that's usually an ignition problem or atiming issue where the fuel is being ignited at the wrong time.
 

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Regarding the question of weather it is popping or backfiring through the carb, here's the best I can describe it. -->> Have you ever heard a firecracker explode underwater? You can feel and tell that some energy has been released, but the noise isgentle, like somebody kicked a soccer ball.



Chris
 

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I went after the timing belts today and I'm very lucky that the engine hasn't destroyed itself! The timing belt slack spec is 3 to 5mm, I had 24mm of slack! The belts were so loose that I was able to remove them by hand without loosening the tensioner pulleys!:shock: The slack amounted to the cams being retarded by about 1/2 a tooth when viewed at the timing marks on the case, with the indicator set to TDC on the engine. Do you think this is enough to cause the problems I have been seeing with the backfiringt up through the carbs?



I also installed new plugs the day before getting in to the timing belts and went for a 40 mile drive. I then removed the plugs and they all were light gray color indication a lean mixture. I'm hoping that the timing belt issue was causing the motor to act lean across the board, otherwise it would tend to be telling me that all the carbs are still restricted somewhere.



Any thoughts???



Chris.
 

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chrisnjillian wrote:
Do you think this is enough to cause the problems I have been seeing with the backfiringt up through the carbs?
The timing belts being THAT loosecan definitely give you a backfire through the carbs. It causes your valves to open at the wrong time. I'm willing to bet that replacing them will solve your issue. :)
 
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