Author Topic: 200 jet? (Read 6455 times)

stroberts22 · « **on:** September 30, 2014, 08:12:33 PM »

I got a thick sleeved, fresh 69.5 bore, ported, stock, cylinder I'm trying to jet. 39 pwk, dgh needle center clip, 52 pilot, 200 main right now and still a little sputter at 3/4 throttle. I started with typical jetting 50 pj, 180 main and it had a bad sputter that I confused with rich but with a plug check I seen it was lean. I decided I was going to find out what will make it rich so I put in the biggest jet I had 200 and it ran better but still 3/4 throttle has that lean sputter but it rev out after I got on the main jet. I ordered a needle to help the 3/4 throttle and maybe get my main back down out of the 200s. Am I on the right track? Anyone ever had to throw that much jet at a stock cylinder? The cylinder is a ebay cylinder from dirt factory but the porting looks like someone knew what they was doing and my engine guy measured it and he said it was close enough to what he does he didn't touch it.

broken1 · « **Reply #1 on:** September 30, 2014, 08:37:27 PM »

I'm not quite in the 200 range but I run a 195 main, 55 pilot & dgh needle in my 39pwk for my 67mm oem heavily ported cylinder & it runs hard for a small bore engine.

C-Leigh Racing · « **Reply #2 on:** September 30, 2014, 09:24:57 PM »

OEM TRX ignition or CR250R ignition ?.

What head you using & how much compression does the engine have.
Pressure checked the engine ?.
Neil

Pumashine · « **Reply #3 on:** September 30, 2014, 09:27:59 PM »

Do you still have the air box lid on?

stroberts22 · « **Reply #4 on:** September 30, 2014, 09:43:30 PM »

Stock ignition, 19cc cool head (engine builder reshaped the insert a bit to get squish right), 175psi on my gauge, holds 7 psi forever on a pressure test, air box lid off. Runs and pulls hard through 1/2 throttle, breaks up a bit through 3/4 then revs after it gets on main.

flynbyu · « **Reply #5 on:** September 30, 2014, 10:17:53 PM »

Just wondering...who was your engine builder?

stroberts22 · « **Reply #6 on:** September 30, 2014, 11:06:05 PM »

Chris Grissom bored it, measured the port timing to make sure it would work, reshaped the head and assembled the top end.

The_Steve_Man · « **Reply #7 on:** October 01, 2014, 07:18:49 AM »

What are you going to use that motor for?

mennis1971 · « **Reply #8 on:** October 01, 2014, 07:19:42 AM »

I'm running a 205 in my ported oem cylinder(with a 40.5 carb). It's a high rpm motor for sure. I love it for when I do supermoto, but it's not a great dune motor IMO(wasn't built to be-it's peaky, kinda like riding a 125 dirtbike). No airbox btw. All I can say is every motor is different, so run what it needs(assuming no air leaks etc...). It used to bother me that it runs such a big pilot (60 or 62) and main. I could play with the carb some and change those(and get my idle back), but it runs great and starts easy. No plug fouling either. The plug actually looks good and just a touch rich. It has to be with the way my R gets wound out for long periods on pavement(or the dunes). Make sure everything is sealed up tight(no leaks-air or anything) and run it is all I can say. Let us know how it runs.

Bowtie316 · « **Reply #9 on:** October 01, 2014, 08:26:16 AM »

Speaking in general, a large carburator on a small motor will require larger jets due to the decreased signal across the venturi. I have no experience with this on these 2 stroke engines however.

C-Leigh Racing · « **Reply #10 on:** October 01, 2014, 11:06:50 AM »

Quote from: stroberts22;43624

Stock ignition, 19cc cool head (engine builder reshaped the insert a bit to get squish right), 175psi on my gauge, holds 7 psi forever on a pressure test, air box lid off. Runs and pulls hard through 1/2 throttle, breaks up a bit through 3/4 then revs after it gets on main.

Ok, got that.
One thing I will say, if Chris G (CGR) is checking it over, you got one of the best laying hands on that engine. I know cause I learned a few things from him.

You could try a tighter gap on the spark plug, say around 18~20 gap & then index the plug so that the gap opening will be pointed to the intake side.
Another thing, sometimes when a dome has been reshaped, specially the bowl area, if the plug tip, when screwed all the way in sticks out into the bowl area to far, it will cause a skip in the upper rpms. Kinda like the spark is getting blown out when the rpms are high. With the plug screwed in, you dont want to see any of the threads on the plug, just the ground strap sticking out into the bowl is all you what to see.

Of all the things I could list, could be making it do like your saying its doing, I would have to say that stock OEM ignition would be what I would focus on.
Neil

stroberts22 · « **Reply #11 on:** October 02, 2014, 08:21:13 PM »

Needle came in the mail today! My arms hurt. LOL