cv carb on my 75 shovelhead

[chopperbelly]

I put a CV carb on my '75 stock shovelhead. It starts and runs great but I can't get any top end out of it, maybe 65 MPH.

[rigidthumper]

Check the rubber diaphragm for a pin hole or pinch- that will keep the slide down, limiting speed/rpm under load.

[Hossamania]

With the air cover off and the bike running, twist the throttle briskly, the slide should lift. If not, see Rigidthumper's response.
If that is not the problem, check your petcock for flow, if you have an inline filter it may be causing problems, check your float.
What size is your main jet?

[76shuvlinoff]

Sorry, have to ask. Top end speed was better before the CV right?

You'll get  it sorted, a CV40 was one of the better things I did for my 76.  Thinking about going back to it.

[chopperbelly]

I'm running a 195 and a 48 for jets. I am very careful with the diaphragm when I put it together.

[JW113]

If the motor is more or less "stock", I think that's a bit too much main jet. The symptom you describe hints at that. I've got a CV on my '77, which is more or less "stock", and am using a 170 main. It will go as fast as you can tolerate the vibration in the bars, 100+.

-JW

[chopperbelly]

I was wondering if it was too big, maybe getting too much fuel

[xlfan]

Might be a bit obvious, but do you get full throttle at the carbs throttle wheel?

[Hossamania]

Might be a bit obvious, but do you get full throttle at the carbs throttle wheel?

Good point, make sure the throttle is opening all the way to the stop.

[Hillside Motorcycle]

Yep.
I'd check the vacuum piston rubber, and 50 pilot, 190 main for starters.
Reason for the large jets in a Shovel, is the fact that the head has such a poor signal.

[dirtymike]

does your intake solid mount to CV carb or is it rubber boot.

[chopperbelly]

How about that back fire through the carb. I'm not a bad wrench but I really suck at carbs, always have.

[PoorUB]

How about that back fire through the carb. I'm not a bad wrench but I really suck at carbs, always have.

Are you getting backfire or cough through the carb? Usually means too lean.

[chopperbelly]

I guess you'd call it a cough. So up on the idle jet?

[Burnout]

Only if it happens on a fully warmed up motor.

You can't make tuning decisions on a cold motor.
If you tune a cold motor it will be dead rich when hot.
You can get it close just going around the block.
The final changes need to be made over time and verified by checking fuel consumption.

It is normal for a cold motor to sneeze and wheeze.

[PoorUB]

I guess you'd call it a cough. So up on the idle jet?

When does it happen? When rolling on the throttle from idle? Richen up the idle will help. A different needle with a smaller diameter at the top will help too.
But like the other post you need to be concerned about how it runs when warmed up. Cold don't matter, leave the enrichener out for another minute on warm up.

[chopperbelly]

fully warmed up it happens

[JW113]

When does it cough, just off idle?

-JW

[chopperbelly]

mostly when I'm just puttin' in 2nd or 3rd. Going along slowly

[JW113]

So... steady speed, very light throttle? And it backfires as in kerBLAM out the exhaust, or more like a sneeze into the air cleaner?

[chopperbelly]

out the carb air cleaner

[JW113]

Sounds like lean on the low speed circuit. Here's a few things you can try.

Increase the pilot jet one size and see if cures the cough.

Closely inspect the transfer ports. They can get carboned up if the bike has been coughing back through the carb, and the problem gradually gets worse.

By the way, what is the outside air temp where you are? Trying to tune in cold weather can be tricky if not futile, depending on the bike.

-JW

[dirtymike]

does your intake solid mount to CV carb or is it rubber boot.

[carioux2008]

I didn't see it mentioned, but have you tried checking the plugs after one of your "65 MPH top speed runs?" That may tell you if your fat or lean and give you a direction to go. Cardboard brown is perfect, gray is lean, black is rich.
Could also be as the others have said, a restriction somewhere or an air leak.

[MikeL]

Had a problem with my 1980 shovel like mentioned. CV also 50 slow 195 main. It started out coughing then popping out carb. Found it was a swelled o-ring. Must of had some gas sitting in the manifold all the ethanol in gas these days deteriorated the o-rings and caused a lean condition.Also the popping singed the o-rings and the slide diaphragm.
If the coughing /popping isn't stopped with a 50 slow jet. I would check your fly weights and see if there stuck and then check those intake o-rings.

                                                                                                       MIKE