i been having a problem with my engine popping back if you shut it off a crank it right back up before it cools down. i replaced the seals twice and it still does it. i just been dealing with it by not starting it right back up. coming home yesterday it sounded like some trash might have got on my needle or something, it didnt want to open up when you gave it all the throttle and sounded a little rough. i took the carb off today to clean it out and i took the vacuum pump out and on one side the plastic looks melted or grooved out and has a lot of carbon buildup around it and all on the slide. do you think this could be whats causing the popping and throttle problem.

 

You must provide some information as to what you are working on...

Year and model bike?

Carb type?

 

What seals?

What does "trash on the needle" sound like?

I don't think your carb has a vacuum pump

Total WAG, but I'm guessing you have a CV carb, and are talking about the slide. If that's what you've got, and it has carbon buildup and has melted in spots, that's not good.

Again, assuming I'm reading between the lines correctly and you've got a carbon-fouled, melted slide in your CV carb, I'd say that isn't what's causing the problem. The problem is whatever caused the carbon-fouled, melted slide.

 

I'm assuming you mean the intake manifold seals? If so they could have been leaking before you changed them causing a vacuum leak creating a lean condition and engine to run hot in which could have caused your carb melting problems

 

yes the seals were the manifold intake, i thought the old seals may have been the reason for the engine pop while cranking it up right after shutting it off like at the gas station. The seals were dry rotted , i replaced them and it didnt help with the pop so i thought i might have just not got it lined up right so i put a another new set on (still pops). My bike is a 1998 heritage classic, stock except for the eagle pipes and the james rocker box gaskets i just replaced in the summer (i bought this bike from a guy in another state so about all i know is its been sitting up for a good while, he was in very bad health and let one of his friends ride it every once in awhile. The carb is the cv that came on it. The bike was running very strong except for the pop a couple weeks ago, i gassed up and the bike sat without being started for about a week and when i went for a ride monday it started fine and i rode to town, it ran fine and on the way home it started running rough, i just thought it might have sucked up something that made it into the carb and caused it to start running rough. So i took the carb apart today to clean it out and when i took the plastic cap off and removed the vacuum pump slide the under side of it had lot of black build up(like candle soot) and the plastic part under the rubber top has a grove on the edge of it like it was melted. The rubber top looks good and it doesn't look dry rotted or has any holes. Im getting a new pump slide the metal on mine looks wore along with the plastic. Going to put that on and try that. I dont know what else to do.

 

Sounds like the carb needs a good once over. Disassembly, cleaning, and record what size the slow. main jet, and float height.

Just have to be careful if you have never done this before. Things like removing the float retaining pin direction (pin gets tapped out with a pin punch in the direction of the arrow cast into the carb), needle jet can be accidentally installed upside down, accelerator pump parts and O-rings, air-mix screw packing O-ring, etc. are all small parts that can be easily lost or installed wrong.

For now, assume your intake manifold seals are OK, and focus in on the carb. Just be aware that when you install the carb, if you have any misalignment of the carb when mounting, it can put torque on the manifold and cause manifold seal leaks. The best way to install new manifold seals is to put the manifold on loose, then install carb with the air cleaner backing plate already installed on the carb, then install the carb backing plate to head bolts, slowly and methodically aligning everything so no uneven torque or tension is being put on the manifold and seals. Also get a new carb to manifold seal...YD

 

Thats the way I replaced the manifold, and I replaced the carb to manifold also. When I replaced the manifold seals the first time I had noticed the bowl gasket was wet so I removed the bowl and sprayed the inside out with carb cleaner and replaced the gasket, put in a new pump and the two tiny o-rings, and the pump shaft rubber grommet. This time I took it apart I removed the pump slide and seen the slide is wore. I took the float off and flushed out the holes with the carb cleaner but I havent removed the jets or the air-mix screw.

 

Sounds like timing to me. Unburnt fuel and a slightly open intake valve.
Does the bike have adjustable pushrods?

 

Slow jet and emulsion tube have extremely small holes in them. That's the first place I look when cleaning a carb. Those have to be physically removed in order to check/clean. The passages that the jets feed also get cleaned with carb cleaner.

Actually, every passage I can find gets carb spray thru it. I spray in the holes and passages using the plastic straw, till I see the spray coming out of the other end of said passage. If I'm not seeing the "other end of the passage" by confirming where the spray is coming out, then I keep looking till I do.

You can use a bic lighter to put 90* bend in the plastic straw to help get the carb cleaner in hard to reach holes like the idle and transfer ports in the throat of the carb. Just gotta keep at it till you can confirm each passage and jet is clean and clear.

It won't hurt to check timing, but gotta make sure the carb is up to snuff also. Focus on one thing at a time. Just spraying up in the bowl area is not a complete cleaning of a carb.

If the slide appears worn, replace it. YD

 

i was hoping to get by without taking the jets out or the air mix screw, but i know everything needs going over. the bike only had 6500 miles on it when i got it last spring so i know it been sitting for some long periods in storage. i was surprised when i took the bowl off that it was so clean looking. i was expecting to find a bowl full of crud. thanks for helping