Jump to content
Sign in to follow this  

Rebuilt engine, still a hard starter...

Recommended Posts

Just done a top end rebuild on my XR400, had valve seats re-cut and all cleaned up by an engineering place, new spark plug, air filter, valve clearances re-done, confirmed auto decomp spring/tube is present, following correct 4 stroke startup procedure etc.

I'm assuming it's due to jetting. I'm at sea level (UK) and the only mods are the spark plug coil resister has been removed, exhaust baffle drilled out and the snorkel has been removed.

My jets are 162/55, does this sound about right? I'm not sure what the float height is set at, assuming stock. Maybe the mixture screw?

Share this post


Link to post
Share on other sites

Is your air filter stock or something like the aftermarket UNI unit?

 

Given the rest of the mods, your pilot is probably too lean for sea level. You should probably be running a 60.

 

You said the spark plug cap resistor has been removed. Did you replace it with anything?

 

Yes, the mixture screw needs to be tuned for your elevation.

 

Be sure you're not running the idle speed too low.

 

You say you're "following correct 4 stroke startup procedure". What would that be? The XR kinda has its own.

 

If you ever have the carb float bowl off for any reason, like changing the pilot jet, the float level specs are 14.5mm minimum drop and 19.5mm max drop.

Share this post


Link to post
Share on other sites

Air filter is a HiFlo foam filter, not sure how this differs from the stock one.

Forgot to mention, I've gone 1mm oversize on the piston too.

Start up procedure, pulling manual decomp and kicking it a few times, releasing it and slowly kicking bringing the lever to the top where it has most resistance and giving it one big swooping kick! (Watched tons of XR400 vids on this).

I've tried increasing idle before startup, makes it a bit easier but still hard to start.

Spark plug resister was removed and replaced with a stainless bolt (was even harder to start before I did this).

I have a new 62 jet but would this be too much?

Edited by alan0259

Share this post


Link to post
Share on other sites

We had two late-models XR250s and both were hard starters.  One of them had a bad plug wire and once that was replaced it became an easy starter.

 

Though the one XR250 was in like-new condition the plug wire core had degraded.

Share this post


Link to post
Share on other sites

Air filter is a HiFlo foam filter, not sure how this differs from the stock one.

Forgot to mention, I've gone 1mm oversize on the piston too.

Start up procedure, pulling manual decomp and kicking it a few times, releasing it and slowly kicking bringing the lever to the top where it has most resistance and giving it one big swooping kick! (Watched tons of XR400 vids on this).

I've tried increasing idle before startup, makes it a bit easier but still hard to start.

Spark plug resister was removed and replaced with a stainless bolt (was even harder to start before I did this).

I have a new 62 jet but would this be too much?

 

The stock filter is a single stage foam over a stainless steel cage that has several layers of wire mesh between 2 screen layers, quite restrictive compared to the aftermarket foam options with their own open cages.

 

You're using choke to start a cold engine, right? Lever all the way up is full choke. All the way down is choke off. Don't touch the throttle. Pay attention to the engine sounds. If you kick it a time or two with choke and it sounds like it's trying to fire , then nothing after that, put the choke to half. Cycle the choke like that, listening for the engine trying to fire.

 

How many turns out from lightly seated is your fuel screw?

 

A 62 pilot may be fine. But answer the fuel screw question above. You may have some room for tuning it to work with the current 55. At least enough to make it start easier and give you an idea of, if and by how much, the pilot should be changed.

 

And I recommend swapping out the stainless bolt in your plug cap with a piece of copper. It has less resistance than SS.

 

Also, everything else being ok, a too low float level will cause hard starting.

 

Here's tutorial for when you work on your carb.

 

Share this post


Link to post
Share on other sites

I've pulled the plug and checked for spark and it seems to spark good so doubt it's this.

I'll check out the carb in the morning.

Edited by alan0259

Share this post


Link to post
Share on other sites

Its a hard starter because of the stupid mikuni carb. Never liked them. Go keihin

 

 If he's right about his current jetting, his carb IS a Keihin.

Share this post


Link to post
Share on other sites

I think the 55 is too small/lean, and that will cause hard starts. I have a 58 at 4200ft, but also have a bigger bore.

The 62 might be too big. The location of the fuel screw will help determine that; if the idle doesn't change as you adjust the fuel screw, you've got the wrong size slow jet.

 

Lean the bike to the side briefly, it will start to puke fuel from the overflow.

Pull decompression lever and roll the engine a few times with the throttle open.

Set to top dead center.

Choke on, throttle off.

KICK.

Edited by boogie_4wheel

Share this post


Link to post
Share on other sites

I am at sea level and a 60 or 62 pilot should be fine. If the temps are a little cold the 62 will probably be best. I have used both on my XR4s. Each bike will be just a tiny bit different than any other. I would stick the 62 in there and tune the fuel screw, after fully warmed up of course. Also a slightly higher idle helps, you can always back it down after it warms up. Sorry, one more thing, I always use full choke when cold.

Edited by YHGEORGE

Share this post


Link to post
Share on other sites

Right! Getting really fed up now of having to stand on my pegs to get it to kick start.

So today I took the 55 pilot out and put the 62 in.

Set the mixture screw to 2 turns out from lightly seated.

Fired it up and let it warm up for a couple of minutes.

I backed the screw out and the revs slowly started to drop. I then put it back to 2 turns out and the revs went back up, then to 1.5 turns and it revved higher, and finally 1 turn and it revved even higher. The revs increase even up to 0.5 turns out but I've heard it shouldn't be less than 1.5 turns, is that right?

I found 1 turn out seems the best when it came to revving it whilst stationary, not been out to ride it yet.

Thoughts? Surely I shouldn't need to go bigger than a 62?

Share this post


Link to post
Share on other sites

When the revs started to drop, that means it was getting too rich. When the revs picked back up as you went back towards 2 turns out, that's highest idle on the rich side. Right around there is where you want to be. Highest/best idle and throttle response off idle, favoring the rich side of your tuning, is what you're looking for.

 

With the amount of change you're seeing in adjustment and the screw range you're seeing it in, I'd say the 62 is close to being the right jet. Tho going from a 58 to a 62 is a 3 size jump, pretty big.

 

The revs keep going up on down to .5 because you're leaning it out.

 

As you play with it more and get to ride it, if fuel screw adjustment stays at 1 turn out for highest/best idle and throttle response off idle, I'd say drop in a 60, so you can get that point closer to 2 turns out. It will at least move it over 1 turn out.

Edited by Trailryder42

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...