HP issues in 107

[rhinoevans]

Posted some HP issues on a DYNO run a few post back (Lost 30 HP and way small main jet). Sent CARB to BOB at XXX for some upgarde mods and here is what he said ::

I HAVE IT APART NOW AND I'M CHECKING IT OUT BUT SO FAR IT DOESN'T LOOK TOO BAD. WHAT DOES LOOK BAD IS THE PROBLEM MAY BE IN THE ENGINE. IT LOOKS LIKE A LOT OF VALVE BLOWBY IS GETTING INTO THE ENRICHENER PASSAGE AND OFF SEASTING THE PLUNGER. THE BLOWBY IS TRAVELING ALL THE WAY TO THE FRONT OF THE CARB AND COMING OUT THE INLET AIR OPENING FOR THE ENRICHENER CIRCUIT. tHE FRONT OF THE BUTTERFLY IS ALL BLACK TO AND IT SHOULD BE CLEAN.

IF THE INSIDE OF THE INTAKE MANIFOLD IS BLACK TOO THEN THATS A PROBLEM BECAUSE IT SHOULD BE CLEAN.

THIS IS WHAT I SEE SO FAR.

BOB
TRIPLE X CARBURETORS


SO, I not much of an engine guy but sounds like an intake valve staying open to long to let flow back into the carb.

Is this as simple as valve / pushrod adjustment? Bike did DYNO at 70 HP. Was going to pull the heads for a Port and Polish anyway. ANy thought on this condition.

 

[woodbutcher]

this sounds like a sully kind of question

 

[rhinoevans]

this sounds like a sully kind of question

Thanks for the help.

 

[alhall88]

The condition could be caused by that,but start with the basics like timing,plugs and wires. What were the changes that occured to drop 30 hp. How long ago was that? If the pushrod adjustment was that far off I would think you would hear a racket.

 

[rhinoevans]

The condition could be caused by that,but start with the basics like timing,plugs and wires. What were the changes that occured to drop 30 hp. How long ago was that? If the pushrod adjustment was that far off I would think you would hear a racket.

I just got this bike from my nephew. The only thing I knew was that it was running rich, so had it dynoed. I knew something was wrong from the small main jet size. No noise/racket. As far as I know the bike rides and runs good (never had a 110 hp bike before so the 70 seemed normal to me), just only 70 HP and a 62 main. So now I know that the extra air is escaping the intake valve and back into the carb, which i guess would account for the samll jet. Could be as simple as a valve adjustment and maybe I need a value job. Like I said , I had planned on a port and polish for the heads anyway, when I changed out the cam to a 600. Thanks for the input.

 

[MARV]

sounds like its sumping, which would cause a big loss of power, and getting blow-by from the crank vented 107 motor.

can do a leak down test to check the valve.

 

[rhinoevans]

sounds like its sumping, which would cause a big loss of power, and getting blow-by from the crank vented 107 motor.

can do a leak down test to check the valve.

Currently I am in CA and will do a compression check when i get back. Also plan to pull the heads to look at the valves, springs, ect. I have no idea what sumping is and not sure what I would look at to see if that is the problem. Could you explain a bit more. Venting, you mean the bottom line from the case that goes to the air filter backplate. Please help before I pull my heads and that is not the problem. Just trying to figure out what would cause valve blow by, whatever that is, that BOB from XXX stated. I know very little about the motor, except that if somthing is in the carb and the intake manifold, and the intake mainfold is BLACK inside but should be clean(I can not confirm this yet, since I am in CA and unable to look at the intake manifold, but from what I remember when I pulled the carb, it was black). Something MUST be coming back into the manifold during the opening of the intalke valve.

Again, I know that 30 hp is alot, however, the big run great with the 70 HP. Not like it is running bad, just the wrong size main jet to achieve the A/F ratio and the loss of about 30 hP. Hard to troubleshoot a bike, from what I know, run good. Thanks again for any help on this matter. Actually looking forward to pulling the heads. Always wanted to do that!!!

Rhino

 

[MARV]

instead of a compression test, which checks cold cranking pressure of the combustion chamber, you need to do a leak down test to see if the valves and rings are sealing.

sumping is when the crankcase is filling with oil that passes a check ball valve at the pump. can drain the case after a ride to see how much oil is in there. should be about 4-7 oz.

do the simple stuff first. plus one at a time so you know the effect.

 

[rhinoevans]

Thaks Marv..Some good advice

Also found this today: Not a comment about my bike, just a post in AMerican Rider

You have a blow-back problem caused by the cam and pipes. The carburetor has little to do with the problem. Even "small" cams close their intake valves later than stock and require a higher engine rpm to prevent the blow-back. The Vance and Hines Longshots are too long and running them without the baffles makes the problem their length creates even worse. Long unbaffled exhausts, especially constant diameter straight pipes, send very strong positive pressure waves back up the pipe. These pressure waves go on through the combustion chamber (during the overlap period when both intake and exhaust valves are open) and make the blow-back worse than it would be if the waves weren't there.

Reinstalling the baffles would help some, but you really need a proper exhaust system. The shorter Vance and Hines Straight Shots with the latest perforated-tube baffles would work better. Their header pipe length and muffler sections are more correct for your engine.



The basic problem is the engine is blowing back some of the air/fuel mixture it has drawn into its cylinders. This is because the intake valves are not closing soon enough to trap the mixture in the cylinders.

This blow-back or "reversion" problem is dependent on engine speed. For each cam design, with its particular intake valve closing event, there is an rpm above which the blow back stops. The sooner the valves close, crankshaft-degree wise, the lower the rpm at which the blow-back stops.

Most aftermarket cam designs aggravate this problem because they close the intake valves later than stock cams. The answer is to either run at a higher engine speeds or fit a set of cams that close the intake valves earlier.

Poorly designed or inappropriate exhaust systems can also increase the amount of blow back, sometimes enormously. The worst offenders are overly long, open straight pipes.

 

[lee]

I think wires are getting crossed here. I think Marv is talking about oil blow by?

 

[MARV]

if you take your filter off and whack the throttle you'll see a puff of fuel vapor exit.

Loafington just started a thread about a longer intake manifold. this theory (i believe) is so this "reversion" of fuel vapor doesnt reach the filter.

30hp loss isnt from your pipes.

check the simplest shit first.

check for sumping?

leak down test?

 

[rhinoevans]

if you take your filter off and whack the throttle you'll see a puff of fuel vapor exit.

Loafington just started a thread about a longer intake manifold. this theory (i believe) is so this "reversion" of fuel vapor doesnt reach the filter.

30hp loss isnt from your pipes.

check the simplest shit first.

check for sumping?

leak down test?

Sumping..that is excess oil in the bottom of the case?? Caused by a falty oil pump?? Would this explain the blow by in the intake mainifold and the drop in size of the main jet??

 

[MARV]

Sumping..that is excess oil in the bottom of the case?? Caused by a falty oil pump?? Would this explain the blow by in the intake mainifold and the drop in size of the main jet??

i'm not saying this is definitely your problem but is a good place to start your trouble shooting.

here's a note on wet sumping I copied.
---------------------------------------------------------------------------
"WET SUMPING
One common problem that scares people is wet sumping. This is basically when you have too much oil in the bottom of the crankcase and it either blows out the breather or the flywheels throws it up on to the piston skirts and the motor smokes like hell or both.

There are a couple of things that will cause this. Most of the time it is because of a check valve in the oil pump that is not seated This is very common in Harley Sportsters built before 1977 and softails fall into this group occasionally, Triumph Twins, and early Norton Commandos are known for this also.

Usually this happens after the bike sits for an extended period of non use. On the older Sportster it usually blows a big puddle of oil out of the breather tube attached to the bottom of the cam cover. Sometimes it will smoke, sometimes not, it just depends how much oil is in the bottom of the motor. Usually if the plugs don't foul, it will clear itself out just by running the motor awhile. If it happens repeatedly at shorter and shorter intervals it is probably time for a new oil pump or at least a rebuild. The problem happens because of the oil tank being higher on the bike than the motor which causes siphoning of the oil into the engine.
On later twin cam engines, a misaligned oil pump can also cause this problem. There have been some issues with a incorrectly installed "O" ring on the oil pump mating surface from the factory which allows engine oil to enter the cam chest cavity and the scavenging section of the oil pump cannot keep up with the task of removing it fast enough. When this happens, you will experience a sluggish engine and possibly engine oil blowing out the breathers. The sluggishness is caused by the flywheels in the motor running through the excess oil in the crank case area.This condition on a newer bike that is under warranty should be taken care of by the dealer under warranty."

 

[rhinoevans]

Update. There is NO black inside the intake manifold, like previously stated. Installed the xXx carb mod from Bob, and the bike started up and ran great. He rejetted it to 74 main. I will take it out tomorrow for a test. Disconneected the lower breather from the carb back plate and ran it to the frame. Not sure at this stage I will pull the heads. I will ride for a day or so and then do a compression and leak down test. Just amazes me on how well the bike run and idles considering it is missing 30 hp!!!!