plug gap help

[barkbuster350r]

Hey guys, I have a 350pv motor that i've had a hard time eliminating a topend wot sputter. I've tried leaning the main jet with no good results. Then I read in a forum that the spark plug should be gapped to 20 thousandths. Checked my plug it was 32 thou, pulled it back to 20 thou and it ran perfect. So I call Allen Knoles at CT, he said never run less than 28 thou. I tryed 28 and it runs like crap again. I have stock ignition probably original, 38 as carb with 190 main, fourth clip on needle, 52 pilot, ngk br8es plug.
Thanks Brad

[beerock]

well, gap it back down then. LOL

you fixed the problem and then unfixed it.It could be a sign of the ignition going, or because of a high compresion spark blow out.

my buddy has a curtis sparks 350 pv and hes running a 178 main. curtis sparks has told me you dont run a large main with the larger cylinders but if you run a big bore pipe on the larger cylinders then you will be around 190.

I would suggest checking your jetting , what you can do is put a new ngk in the bike(br8es) and warm it up and hit WOT and see if it still breaking up. if it is try a 185 main if it clears up more go to a 180.

what elevation are you at?

[barkbuster350r]

I assumed that it is high compression blowout, but why was I told not to run under 28 thou on my gap. Can it cause any damage to run too small of a gap?


I'm running a paul turner eliminator pipe and my elevation is about 1000 ft. My plug looked good with a 190 main jet and gapped at 20 thou.

Thanks, Brad

[beerock]

you need a big bore pipe and if your at 1000ft then what is your port job like? is it bottom mid or top end ported?

i think you should try a 180 and see what it feels like from what my buddy told me, each time he went down on the jet the motor got stronger and stronger, then he put a 178 in it and its a monster. Also, WHat NEEDLE are you running? a dgh?

[barkbuster350r]

I have a mid range port job and I have a dgh needle. And I've always been afraid of leaning past a 185 main jet because Allan at CT had told me that even with the humidity in Arkansas I should never run leaner than 185. Maybe he's crazy?

Thanks, Brad

[beerock]

putting a 180 in it and checking with a new plug wont hurt anything. if it is poping and cuttign out its to lean.

I doubt the ct motor has a better port job then my buddies Curtis sparks pv, unless your good friends with allen, hes not porting your motor.

even still a 180 at 1000 ft is prolly to rich but will probably run ok.
When you check a plug you have to look inside the metal were the porcelain joins the metal down inside the spark plug. thats where you tell if its jetted right, and i bet its black inside the plug.

do like i said, run it with the old main and plug. then switch the plug to a new one and put a 180 in it. at 100 feet i would say a 175- 178 should be right. just make sure you check the plug correctly.

[barkbuster350r]

how should i gap the plug? 28 thou?

thanks, brad

[beerock]

I would buy a new plug and just throw it in the R I always have, thats because i change them very frequently , not because i foul plugs, just because I can. If you continue to have a sputter when you put in the 180 then gap it down to 18 or 20 thou put a new lug in it again and check the jetting again.

[TRX370R]

I run my br8es at .018 and haven't had a problem. If I gap it any bigger then that it starts to sputter at upper RPMs in 4th and 5th gear. I closed up the gap due to a suggestion by ESR. They said that the stock TRX ignition simply doesn't but out enough voltage to fire a big bore/high compression engine when cylinder pressures are so high. So I could either close up the gap some or purchase there CR style ignition system for $500 and lose my lighting system. I took the free route. By the way I am running a 40.5mm carb with a 190 main at sea level (Pismo Dunes)

[barkbuster350r]

Thanks for the info trx370r. By the way, do you have an extended swingarm on your 370? I'm running stock 88 length on my 350 and it's a handful in the sand. I can't do any good drag racing.

Thanks, Brad

[beerock]

Originally posted by TRX370R
I run my br8es at .018 and haven't had a problem. If I gap it any bigger then that it starts to sputter at upper RPMs in 4th and 5th gear. I closed up the gap due to a suggestion by ESR. They said that the stock TRX ignition simply doesn't but out enough voltage to fire a big bore/high compression engine when cylinder pressures are so high. So I could either close up the gap some or purchase there CR style ignition system for $500 and lose my lighting system. I took the free route. By the way I am running a 40.5mm carb with a 190 main at sea level (Pismo Dunes)

what style pipe do you have

[barkbuster350r]

paul turner eliminator pipe... this is what duncan racing says about it on their website...........

Power Curve:Good low-end response with a very strong midrange pull. Top end power very good, especially when considering how much midrange power is delivered.
Designed to fill the void between Midrange and High Rev pipe. Has better top end than the famous TRX RACE pipe but sacrifices a little smoothness. Also gives more rideable bottom and midrange than the TRX High Rev Pipe.
Provides the most Midrange/Top End power Combo of any TRX 250R pipe on the market today.

I've always loved duncans pipes.

[beerock]

i meant trx370r

[ESR250R]

my lrd ported motor also did this. i gapped it down to 18 thousanths and it ran great (was recommend by lrd for high compression motor) they told me i could gain a little if i went with the cr ignition and a bigger gap but i think i will just stick with the free route as well. btw i have a 190 main on my 265 lrd motor. with a 38mm a/s carb. and i am at 700 ft above sealevel.

[TRX370R]

I'm currently running a ESR TRX5 with the centermount silencer. I was using a Curtis Sparks HiRev Big Bore Pipe also. Had the top end sputtering with each pipe and was cured by changing the plug gap. For the swinger I am running a Lonestar +4 and +2 +1 A-Arms up front. I have been very happy with this combo being that it is a dune only bike. When dragging I can launch hard in 2nd without the front end coming up, but if I want to hang them up there all you have to do is lean back alittle bit.

[Dave83]

I run mine right at .020 on my 310.I ran my .050 over stock cylinder there to.The stock cylinder would make right at 220 psi with fresh rings and would get the top end sputter.Found the gap solution and it has worked ever since.

[beerock]

Originally posted by TRX370R
I'm currently running a ESR TRX5 with the centermount silencer. I was using a Curtis Sparks HiRev Big Bore Pipe also. Had the top end sputtering with each pipe and was cured by changing the plug gap. For the swinger I am running a Lonestar +4 and +2 +1 A-Arms up front. I have been very happy with this combo being that it is a dune only bike. When dragging I can launch hard in 2nd without the front end coming up, but if I want to hang them up there all you have to do is lean back alittle bit.

wnna sell your big bore csr if your not using it?

[wilkin250r]

The only thing I would add is to be careful with your plug reading and jetting at WOT.

2-strokes are funny. Your mid-range RPM mixture is different than high RPM mixture. I'm not talking mid-throttle, that depends on your needle. I'm talking full, WOT, there is a difference in your mixture depending on how much air you're pulling through the carb, which varies with RPM.

2-strokes are known to be rich at high revs. That's why many of the dirtbikes have Powerjets, they have a separate, small fuel jet that cuts out at high RPMS and leans out the mixture.

So what's the point? Well, if you do your plug chops at high RPM, and jet for spot-on, you're going to be lean in mid-range.

[beerock]

you suppose to jet from WOT (main) and then back to 3/4(needle)

have to get the main right before anything else can be tuned.

[wilkin250r]

Right, but it has nothing to do with throttle position.

High-RPMs will be richer than mid-RPMs. If you do a plug chop at max revs, and jet it spot-on, it will be lean at mid-RPMs, regardless of what throttle postion you are at (WOT or 3/4)

Throttle position and RPMS are two different things.

Now, if you hold it at WOT, you shouldn't be in the mid-RPMs very long. Most likely, you'll reach high RPMs real quick. So, my advice, jet a little rich.

It's kinda hard to hold WOT and keep the engine in mid-RPMs.

[barkbuster350r]

I appreciate all the advice from you guys... you've been a lot of help. I always jet my quads a little fat for peace of mind. Thanks again!

[TRX370R]

Originally posted by beerock
wnna sell your big bore csr if your not using it?

Sorry but I actually sold it on Ebay a couple months back to someone from the UK. It has seen better days though......the mount was torn off at one time and rewelded, chrome was bad and had some dents.

[beerock]

Originally posted by wilkin250r
Right, but it has nothing to do with throttle position.

High-RPMs will be richer than mid-RPMs. If you do a plug chop at max revs, and jet it spot-on, it will be lean at mid-RPMs, regardless of what throttle postion you are at (WOT or 3/4)

Throttle position and RPMS are two different things.

Now, if you hold it at WOT, you shouldn't be in the mid-RPMs very long. Most likely, you'll reach high RPMs real quick. So, my advice, jet a little rich.

It's kinda hard to hold WOT and keep the engine in mid-RPMs.

No it wont, thats what the needle is for. to jet for 1/4 to 3/4 throttle operation