Loss of Acceleration / Power, TC88 Carb'd

trikes4ever · Nov 24, 2010

I experienced a sudden loss of power and acceleration today. Engine seems like it is laboring most of the time. Acceleration is about like a Honda 305. It starts fine, idles fine, takes off and cruises at 60 but feels like it's lugging all the time, acceleration is terrible, opening throttle completely accelerates, but just barely. I went to pass someone this morning, down-shifted to 4th at about 55, and had trouble getting around them. At one instance - after stopping for about 15 minutes - it seemed OK for a few minutes, then the behavior returned. I dropped the bowl off the bottom of the carb and no signs of any crud. 
 
I have to think this is a sensor or electrical problem of some kind - seems like it's not getting any timing advance - I compare it to and older car with vacuum advance distributor with the vacuum disconnected. Runs fine - just no power. I can still drive it - but it's borderline embarrassing it's such a slug. Applying throttle make a little more noise but doesn't do much else. 
 
Any clues on where I should start looking?

I'm thinking an intermittent electrical connection, but just don't know where to start.

CadtoChrome · Nov 24, 2010

Have you got a stock ignition? (single fire)
Take a look at the plugs, what do they look like?
Do you have any miss or pop accelerating or de-accelerating?
Does your exhaust pipes seem to be hotter than normal or about normal?

answers to these may help in figuring out your problem.

Regards,
Chuck

trikes4ever · Nov 24, 2010

Stock ignition. New plugs today - old ones were lightly carboned. No missing, no popping, maybe a little on the rich side - 190 main jet - plan on addressing this when I install new exhaust next week (V&H Big Radius 2-1), but prefer to be a little on the rich side rather than the lean side. Pipes are normal - no change in temp or color. Light carbon in pipes.

I'm wondering if it might be MAP sensor? Or connection to MAP sensor? Will take it to my indy Fri or Sat if I can't figure it out.

trikes4ever · Nov 29, 2010

Found the problem. I figured I'd exhaust everything I could do before taking her into the stealer, so removed the carb yesterday. Not sure what needle but there was one washer under it. When I pulled the slide I noticed a small tear in the diaphragm just inside the seal - ah-ha! Took a ride to my indy and he had a few in his junk box, one with no pinholes or slits, so brought that home, cleaned up, and installed. She runs better now than since I purchased her in May so I expect there was a small pinhole that recently grew, probably since I've had her. Can't explain why it was intermittent though. At any rate, she fixed and really pulls now. I'm holding off fine tuning until I install the new V&H Big Radius 2-1 which should be later today. 
 
Right now the mixture screw wants to be almost closed, so I'll probably want to remove the single washer from under the needle to lean her up a bit and get the mixture screw in range, but want to see how she is with the new exhaust first. There's a 190 main and 45 slow in there now - factory. 
 
Not sure what the needle is, but it's not a Dynojet (no C-clip).

When I take it apart again I'll take the needle to my indy and see if he can tell if it's factory or a Sportster needle. If anyone knows an obvious way to tell I'd appreciate hearing about it.

trikes4ever · Dec 12, 2010

Just can't leave stuff alone. Concluded yesterday that my float level is too high. I've been experimenting with slow jets and mixture adjustment and it just has not responded like it should to these. Realized after dropping the bowl very carefully yesterday while holding the carb level - and still dripping quite a bit of fuel - that my float level is too high. Float level effects all other adjustments in all circuits. My fuel economy has not been what it used to be. I expect I inadvertently 'adjusted' it in one of the many times I've had it apart over the past week. Harley instructions are not exactly crystal clear on this subject, but will take a stab today when it warms up a little. I know the fuel level should be at or below the sealing flange surface but coming across an actual number on fuel height has proved to be impossible. If anybody knows this number I'd appreciate the info. 
 
It's a CV40 carb - number should be the same regardless of bike.

This should be a Keihin spec, not a Harley spec.

1550vt · Dec 12, 2010

There is a specific angle the CV carb should be tilted to make the float lift off/sit in the seat at the correct "moment". The stealerships had/have a jig to sit the carb on and properly adjust the float. I use to have one I made around here out of a block of wood, but it's long gone now. I want to think something around 50-55 degrees, but I am not sure. I will do some looking, but I'd just go to a search engine and search out..."how to set the float-level on a CV carb." and see what you come up with.

I'll poke around too, but I would think this procedure would be in the service manual and surprised it's not...if you say so. I usually used the trial-n-error method. I am sure you have checked your seat and needle valve?

1550vt · Dec 12, 2010

Well....I was off quite a bit...it's 18-degrees. I am attaching a (rather poor quality) picture and a narrative on how to perform this adjustment.

I can't seem to get the narrative to post, but if you go poke around like I suggested....you will find it. The diagram attached shows that block of wood and the correct angle is 18-degrees.

trikes4ever · Dec 12, 2010

Thanks - and it is in the manual. I think I have it straight in my head now. It's a pretty short narrative with 3 illustrations - which were confusing to me. What I was wrestling with was the one with the carb at the correct angle and the position of the float valve pin and tab - it looks like the pin is depressed some in the illustration, but I believe they are showing the tab actually over it, so my thinking is the correct position is to have the tab just touching the pin but not depressing it at 15-20 deg, 0.413 - 0.453 from float edge to O-ring flange surface. Thanx for the response! Now I'll just print out a 17.5 degree wedge and go to work.

1550vt · Dec 12, 2010

Just position the intake side (part that plugs into the manifold) as shown in the picture....down on top of that angle-block with the float pointing down-hill and the inlet pointing up-hill. Make your measurements and bend the tab on the float to get the correct specified measurement. 
 
I usually used the trial-n-error method, until I installed the first turbo in town on a 97 EVO. All the guys at the dealership were really interested in my project and the thing was EXTREMELY sensitive to carburetor settings. The service manager was the one that showed me how to do this right with the jig. 
 
You can jet around a slightly-off float setting, but not if it's way off and actually flooding. If it's flooding....it's set too high or you have some issue with the seat, plunger, float or even the bowl gasket. best thing to do is "by-the-book" with the float setting first and then fine tune with your jetting and read those plugs. 
 
Most of the guys that still have the carbs around here let me fool with them (when they can talk me into it). I can generally tune one to get around 44-45 MPG and that's hanging almost on the too lean edge, but they get terrific fuel mileage. If you are looking for performance...bigger jets and more fuel doesn't always equal the answer. I have had 2-barrel V8's run circles around 4-barrel V8's. It's just a matter of the mixture and too much gas is just as bad as not enough...maybe worse. 
 
About that busted diaphragm..... 
 
never allow the bike to back-fire, spit, or sputter very much or you will pop that diaphragm.

In your case....the slide was not coming all the way up (or maybe not at all). The slide is not directly controlled buy the throttle cables, it's controlled by differences in vacuum in the venturi. If that diaphragm is ruptured or leaking...the slide won't come up. 
 
Good luck!

trikes4ever · Dec 12, 2010

I went after the float setting as I just replaced pipes and there was carbon in the heads, in addition to the mileage being poor. Just finished adjusting the tab on the float and it was letting in too much fuel You'd think with something that's this important that there would be a better way to adjust it. Will probably brave the cold a little later and see how it behaves. I'm presently running a 190 main and 44 slow - just dropped from 45 to 44 to get the mixture screw in range. Also stock needle, although I have the CV Performance needle which I will try out when I get everything else stable. I was way off on my interpretation of the HD procedure - it's not when the tab touches the pin - it's when the valve barely closes. I guess this is how they chose the angle - valve just closed without spring compression under the weight of the float, float parallel to sealing surface. Seems like you could just eyeball this if you knew exactly what they were trying to accomplish - that's how my indy does them. 
 
Appreciate your comments.

trikes4ever · Dec 12, 2010

Took a short run with the adjusted float. There's a definite difference - very slow to warm up, and sputtered a couple times - even after it warmed up. It' has never sputtered the entire time I've owned it. Got home and pulled the 44 slow jet and put the 45 back in and re-adjusted the idle. It idles much better with the 45. Had definite signs of idle / low speed circuit problem during the ride - sluggish just off idle and didn't return to stable idle for a few secs after stopping. Full throttle performance was fine - no hesitation, no starving, so I don't think the float level is too low. Today's run was about 50 miles - 43 MPG, but not a very good test with this few miles. It was very windy and about 50 degrees outside. Didn't see too many bikes. This is up from 35 on my last tankful. Will run a tank through tomorrow to see if the sputtering is gone and check mileage again. I don't expect to get back to the best I've done with this bike (48 mpg) because of the added weight and wind resistance (trike, full windshield) but 35 really sucked. Progress!