Carburation

[DGXSER]

The problem/performance - Idles somewhat irratic, runs fine when on the throttle through all RPM ranges, plenty of power no backfires or misses I can discern. When decelerating, exhaust pops alot. At idle, no exhaust popping. When maintaining throttle at 3,000 RPM and below, sputters, just a little, enough I can hear it but nothing that translates to the wheel. Nothing I can nail down to a miss of one cylinder.

Diagnostics so far - compression is between 156 and 142 on all four. All four plugs are tannish brown at the tips and on the insulator. All four show a bit of black toward the bottom of the insulator and on the thread ring exposed to the cylinder No 2 slightly more than the others but all four the electrode tip and the top of insulator are tan brown.

Measures so far - Put about 2/5 a can of sea foam into about 3 gallons of gas in tank, ran 2 gallons worth through, filled the tank, added the rest of the can then ran about a gallon out and put a fesh gallon in it. (It was to nice a day to leave it parked after I got back, will be to long before we get another. That and I thought I got the sea foam concentration a bit high and wanted to "Water" it down).

Based upon what I have read in different threads, I plan to check my timing and see if I can adjust if needed, someone indicated the 81 specials you can not adjust timing?

Also expect the pilots are the culprits. Trying to figure if I should just give seafoam time to open up the pilots or take the carbs off and clean them. I like the theory of "if it ain't broke don't fix it", and I dont want to mess with the floats if I do not have to. If I give the sea foam a chance, how long is enough? to much?

[nebr1100]

Backfires are sometimes caused by a vacuum leaks. Spray some WD-40 around the carb holders and vacuum caps and see if the idle changes, could be sucking air between the carb holder and the head. If the RPM changes you have a vacuum leak, remove carb holders and RTV Silicone the carb holder surface to the head. It solved the problem for me.

[prometheus578]

"You're not running on all cylinders...

and neither is your bike."

When decelerating, exhaust pops alot

Often indicates a lean condition.

Idles somewhat irratic

I think you've got an idle circuit plugged some where.
Get some water or something like a spray bottle of 409 and spray the header pipes while the engine is warm and at idle.
I believe you'll find that one of the pipes won't "sizzle" like the other three do.
If that's the case... pull the carbs for a cleaning.

[planedick]

Don't forget

Synchronizing the carbs after cleaning and adjusting will make a world of difference.

[dbeardslee]

Don - If you didn't synch after cleaning you could be hearing all kinds of wierd stuff coming from the motor. If you need some help, I'm up here in Maineville close to Kings Island. I've got the gauges and a colortune plug.

On the seafoam, about 1/3rd of a can in a full tank should do it. One twelve ounce can is supposed to treat 8-20 gallons. Try to keep the rpms down when you're running it through so it gets the low idle circuit nice and clean. Do you still have the octopus connected? What kind of condition is the inside of your tank in - rusty? Line filters installed?

You're right about the timing, but some of the 81's have a little adjustment. When you check it, make sure you disconnect your vacuum advance and plug it at the carb tap. A couple degrees made a very noticeable difference on mine. I set it dead on 10 degrees BTDC and now I only get a very light back-rap if I decel real hard.

My $.02

[oldyam80sg]

I have found that the bread tie sync will get you started.At very least it will get you able to ride it.I had to clean out the carbs at least 8 times before i got it clean.Good luck!

[DGXSER]

Thanks all the great information,

I spprayed carb cleaner all around the intake boots, no change.

I let the bike warm up and took it for a 2 mile warm up ride, then sprayed all four headers with a water mist up close to the heads. All four sizzled pretty good, althought he water did stay on #2 header a very little bit longer than the others, it is also the cylinder with 142 compression while the others were 150-156, and the one with a slight bit more carbon than the others.

DBeardslee,
Thanks for much for the offer to help. I may take you up on that. I eliminated the octy on my bike. The tank does not look rusty in my opinion, but it certainly does not look brand new either. After I did the gear fix when I put the tank back on and fired it up (after emptying the tank to test the theory of prime using reserve) it did run like crap at first like it was only hitting two or maybe three cylinders and then cleared up after running a few minutes. I have not put the in-line filters on yet. Still trying to figure out a space for them.

One thing I did notice today is that my right side exhaust does not have the same sound level or the pressue of exhaust coming out of it as the left. Although those are the cylinders with the highest compression. I know there is a crossover so in my opinion exhaust form either side could be from any of the four cylinders. Perhaps I need to check my exhaust for blockage? I would think that a lean condition or blocked exhaust would show up at the plugs though.

[skids]

Another place to check for leaks is at the exhaust gaskets. Also make sure that the welds under the heat shields are not cracked, Specials are bad for that. (or did you say you had an aftermarket system?)

[skids]

You know, if the pilot system is not really running perfectly (with the pilot screws to help compensate the adjustments) running the bike at other throttle positions starts running with fuel feeds through the pinholes in the tops of the carb throats, and with the main jets. It will naturally run better while riding if the pilot circuit is the only problem. Also, if the carbon fouling occurs with variable throttle positions, you only know that there could be an issue, you can't pin it down to the pilot screws or necessarily to the synch. First things first... you checked for leaks. Now check the synch and retest. Then adjust the pilot screw a little at a time, keeping track of how many quarter turns (at first). As far as fuel filters, Fram makes a narrow one for inline filtering. Run the line from the right petcock to the left and the left petcock to the right side. There is plenty of room.

[Cobia]

Me thinks that it's carbs cleaning time

Hey DGXSER,
I read nowhere on the thread that you've disassembled and cleaned the carbs. If you are not absolutely positive that the carbs are as clean as you can get them, that would be my starting point. Believe me when I tell you that most engine performance troubles on these bikes are solved by having clean and properly adjusted carbs. That includes synching.

[tarzan]

After reading this whole post it sounds like you ended up with junk from the tank in the carbs and plugged up an idle circuit or at least something in the carbs..Also you may want to pull your petcocks and make sure the towers arent torn and letting stuff past.Or you could put inline filters like a lot of guys here do.I dont, but my tank is clean inside and I put new towers on the petcocks.
It carb cleaning time!At least its winter,what else do you have to do?

[Larrym]

If carb dissassembly/cleaning don't make the problem go away and you're still looking at your carbs as the likely suspect then I have a test carb bank that I recently built/synched to diagnose a problem my bike had. Turned out that my problem wasn't the carbs.

Will make the carb bank available after the holidays as I'm just now headed out to "travel" in these foul weather conditions.

You pay the shipping both ways. No "disassembly" of the test carb bank. Just plug and play: will run better or the same after the swap. Nice way to know for sure whether the carbs "be or not be" the problem.

carbs are for/from 78/79.

[DGXSER]

Carbs are out

Larry,

Thanks for the offer of using the test carbs! I have just completed pulling mine out of the bike.

Now I understand why some have tossed the stock airbox. I thought the countershaft was a tight fit!

Now to the task of cleaning. I never had a carb torn down before so I am taking lots of pictures and going very slowly. Some of those pins holding the floats in place are VERY tight, I do NOT want to break the post off!

I am using the carb maintenance threads as my guide. Although I have to really wonder what the BFH in the pic of tools would be used for on a carb? Perhaps that is for when it gets really screed up you just pound into oblivion? I have the float bowls opened. Stopped there to slow down and take a break, get the camera so I make sure and record how things are in there now. I have an assortment of screwdrivers, but I do not own a metric rule yet so I need to get a good one to measure float height.

[DGXSER]

Carb Differences

OK, I am wokring on just one carb right now till I figure it all out so if I mees one up I got otheres to look at to get ti back right.

I have a couple items that differ form my clymer maual and the thread on carb removal and cleaning. MY float neddle goe into a brass tube that is held down with a phillips screw and a "plate" that goes over it. Does that piece pull out, or unthread somehow? Also do not se ehow to get the diaphram needle valve seat out from the main jet side.

Any other differences I should be aware of for the 81 special from the clymer manual or the tech tips?

Thanks for all the great knowledge and help!

[DiverRay]

Here is a start:

MY float neddle goe into a brass tube that is held down with a phillips screw and a "plate" that goes over it.

You need to pull the screw, and use a pair of needle nose pliers to remove the seat/brass tube. There is an "O" ring the MUST be replaced, and should be part of the kit you have. You did buy a parts kit for the rebuild??
Second part:

Also do not see how to get the diaphram needle valve seat out from the main jet side.

If you are talking about the brass looking part the needle fits into when the diaphram is closed, that is the emulsion tube. To remove it, you remove the main jet and the washer under it and using a dowel or small block of wood, TAP it with a hammer. It will come out into the venturi area of the carb ( push toward the diapham ). Sometimes you will find a little carb cleaner sprayed around the tube will help loosen the old gas.
HTH