Start up promlems w/ Trailmaster xrs 150

[Mydive2]

Installed new stock carb, fueltank valve, hoses
and filter and fresh gas. Started right up, ran like a champ after installs. Next day, will not start. Getting plenty of gas at carb fuel inlet. Cranked and cranked. Pull plug to check for spark, which it does have , but spark plug dry as a bone. Found it will start with a squirt of starting fluid and will then run like a champ. Ran it for 30 min., shut off and restarted repeatedly, no problem. Let set for two hours, would not start again without starting fluid. As before, ran beautiful. I'm beginning to wonder if it is a vacuum problem at the low rpms during cranking. Suspecting vacuum leak at the original rubber intake manifold.

 

[Hellion]

Are you using choke for starting? It is an absolute must for starting most carbureted engines at least in my experience. I see it time and time again on YouTube with all the neophytes and their new atv, minibike etc., crank-crank-crank and no start, then they invariably remember to apply the choke and it suddenly roars to life.

Then again you have people who don’t know this, never learn it, so they tune the carb to run rich at all times so it will start to their liking and they foul their plugs; black and sooty. What does your spark plug look like and do you know how to read spark plugs?

 

[Mydive2]

It's a new carb with stock electric choke. I swapped out the previous carb which had a manual choke installed. Same problem both carbs. I think there is a vacuum leak at the rubber intake manifold. Won't draw enough vacuum at low cranking rpms to pull fuel through the carb jets. Probably why it will run great when started with starting fluid. It will start up without fluid when warmed up. Manifold expands under heat to seal leaks, imo

 

[Karttekk]

Grab a can of carb or brake cleaner, start the engine cold then spray cleaner around the base of the intake and see if the RPM's change. This will tell you if it's sucking air through a bad base gasket or rubber seal. New intake manifolds are available. Could be a hairline crack in the manifold also.