R&D's P-38 Lighting for FCR Carb. Need Advise
- Thread starter MoGwai
- Start date
What it does, is limit the duration of the accelerator pump spray by stopping the diaphragm. Supposedly and with some evidence to back it up, it eliminated the rich bog you sometimes get when whacking the throttle from closed to WFO very fast.
I achieved the same effect by modifying the internals of a very small electrical connector block that I attached to the rod that goes in the pump to squeeze the diaphragm.
When you get the cover or in some other way shorten the duration of the spray, you will probably want to go to a richer clip position on the needle.
I achieved the same effect by modifying the internals of a very small electrical connector block that I attached to the rod that goes in the pump to squeeze the diaphragm.
When you get the cover or in some other way shorten the duration of the spray, you will probably want to go to a richer clip position on the needle.
Strick
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- Nov 8, 1999
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I have the p-38 and it works. You can also pinch the chrome fork prongs together that lie just behind the black dog leg on the right side of the carb. This is the mechanism for the accelerator pump. By pinching the fork prongs together it will limit the a/p spray (duration). You can accomplish this mod without removing anything in probably 10 seconds. You just won't know how much effect it had on the a/p squirt, without removing the carb.
Good LucK!
Good LucK!
BTW, just pinching the forks may have a sligthly different effect. As per Keihin's recommendation the accelerator pump also has a "delay" when the throttle is opened, i.e. there is some play between the black plastic lever and the rod. If you have this play (my -02 520 SX didn't) and you pinch the fork, the play will first be eliminated and only after that is the duration affected (before that it just moves to a different throttle opening).
What I have done now is to create some play by putting some tape over the fork (the same effect as spreading it) and use the connector block to limit spray duration to about 1 second. I won't know how it really works until we get to summer and conditions that stress the engine a bit more than ice.
What I have done now is to create some play by putting some tape over the fork (the same effect as spreading it) and use the connector block to limit spray duration to about 1 second. I won't know how it really works until we get to summer and conditions that stress the engine a bit more than ice.
Strick
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When you say you are taping it to increase the contact area, I am assuming you are doing that in conjunction with the other 'electrical connector mod'. By opening the fork it looks to me (upon inspection) that is would have no effect on the amount of spray or the duration of spray. This is without any other mods.
It is my understanding from reading 'Taffy's' explanation of his electrical connector mod, that in fact it does the same thing as the P-38, which makes sense to me.
Pinching the fork prongs together did limit the spray on the '02 400SX I did this on to ~ 1 second. I would be willing to try the connector mod, but I have no idea how to get my hands on one of those things.
It is my understanding from reading 'Taffy's' explanation of his electrical connector mod, that in fact it does the same thing as the P-38, which makes sense to me.
Pinching the fork prongs together did limit the spray on the '02 400SX I did this on to ~ 1 second. I would be willing to try the connector mod, but I have no idea how to get my hands on one of those things.
This is the deal: when my bike (and at least some others) came from the factory, the black lever already puts some preload on the rod i.e. the diaphragm is slightly compressed with the throttle fully close. If you look closely, the hole in the black lever where the rod connects is oval, not perfectly round.
So when you open the fork, you will get some play in there and therefore make the spray start at a later time, and if there was actual preload, lengthen the duration. Then I have to do the electrical connector mod to reduce the duration even more than I would have to without the tape mod (because the rod will start from a greater "height" since previously it was preloaded).
To make matters even more fun, the rubber boot thingy over the rod pushes the rod up, and if the black lever allows the rod to move high enough, actually pushes the rod off from contact with the diaphragm. This has no effect in actual operation, but makes the adjusting part harder, so I do the adjusting without the boot.
Check out http://www.keihin-us.com/tune.html
Those connectors you can get from pretty much any old electrics store. They are the stuff that at least here in Finland were used to connect your lamps(as in the ceiling inside your house) to the wires that came out of the ceiling before they got the plug-and play-connectors. Then you just have to use a hobby knife to cut the metal part from inside the plastic block (they usually come in a bigger block with several connectors).
- Thread starter
- #7
Still cant quite get it there from all you guys explainations:confused:
So is the P-38 a good buy or what? I'm using a SX muffler with a main jet of 178 or 180 I think.(forget what the machanic said):think
I'm only 5ft4in at 59kg and trying to improve the susp. n have a longer rev range for my bike,so I'm having the WP revalve kit and thinking about this P-38 thingy with the Wolf CDI for 4stroke and Scotts damper on the way.
What you guys think,any advise or comments? Thanks;)
So is the P-38 a good buy or what? I'm using a SX muffler with a main jet of 178 or 180 I think.(forget what the machanic said):think
I'm only 5ft4in at 59kg and trying to improve the susp. n have a longer rev range for my bike,so I'm having the WP revalve kit and thinking about this P-38 thingy with the Wolf CDI for 4stroke and Scotts damper on the way.
What you guys think,any advise or comments? Thanks;)
What Anssi said about the play or delay in the fork is correct and it's intention is to keep the stream of fuel from hitting the slide before it moves up out of the way. On my '01 400SX, this was not a problem. I pinched the forks together to get about 1 second of flow. As a precaution, watch the fuel stream to make sure it doesn't hit the slide. I have a P-38 plate and can't feel any difference when both are PROPERLY set up. The reason I empasize properly is that I got my P-38 and just slapped it on. The result was a fully dissabled accelorator pump! Not every carb is the same so it's not a true bolt on and forget item. I ended up haveing to adjust the fork to get the P-38 to work which is why I ended up experimenting without it. As Anssi also stated, the rubber bootie on the rod will play games with you!!! It had me going in circles until I figured out what was going on. Now I make sure it's extended all the way before doing my adjustments. The bottom line is there are a couple of ways to skin this cat....adjusting the fork, electrical connector or P-38. But all of them will require some attention and possibly fine tuning to insure that the modification is working as intended! Good luck!!
Strick,
Was your first P-38 labeled as a KTM specific unit? I remember reading about someone haveing tryied the 400/426 part and it caused problems, but I couldn't remember if that was you. Anyhow, the funny part about my situation is the package was clearly labeled for the KTM. Maybe they got a 426 part in with a batch for the KTMs? Regardless, I think the lesson with all this is that you shouldn't mess with the AP unless you are prepared to do it correctly and observe the squirt.
Was your first P-38 labeled as a KTM specific unit? I remember reading about someone haveing tryied the 400/426 part and it caused problems, but I couldn't remember if that was you. Anyhow, the funny part about my situation is the package was clearly labeled for the KTM. Maybe they got a 426 part in with a batch for the KTMs? Regardless, I think the lesson with all this is that you shouldn't mess with the AP unless you are prepared to do it correctly and observe the squirt.
Guys-
I put together a website with detailed instructions on the A/P mod, as well as other established jetting improvements. I have not personally tried the P-38, but I'n not sold on it's superiority over the simple "fork mod" either.
Go to:
.www.x1networks.com/rfs.htm
The site is inside a 384/128k line so be patient if it loads a little slow. I hope this is helpful to anyone looking to give it a try. ;)
I put together a website with detailed instructions on the A/P mod, as well as other established jetting improvements. I have not personally tried the P-38, but I'n not sold on it's superiority over the simple "fork mod" either.
Go to:
.www.x1networks.com/rfs.htm
The site is inside a 384/128k line so be patient if it loads a little slow. I hope this is helpful to anyone looking to give it a try. ;)
Strick
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Bud-Man, mine was actually labelled wrong, but the labeling was discovered later on the invoice, after installation. I later took off the carb to time and Viola` no squirt!
AFM744, I am going to check out your site right now. AND I agree with you also. There are ways around the P-38 mod. I just happended to buy it before I discovered any other way.
AFM - that web site of your's is terrific! Check your PM. And THANKS!
AFM744, I am going to check out your site right now. AND I agree with you also. There are ways around the P-38 mod. I just happended to buy it before I discovered any other way.
AFM - that web site of your's is terrific! Check your PM. And THANKS!
Last edited:
OLD STROKER
Member
- Feb 19, 2001
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Jon
Just saw your web site for the first time. It's great! Keep up the good work.
Bob.
Just saw your web site for the first time. It's great! Keep up the good work.
Bob.
Gents-
I gave some thought to Anssi's point about the "delay", i.e. the A/P doesn't start to squirt until you've already got the throttle open some. Sooo, I pulled my carb, UN-pinched the fork and pulled out the A/P pushrod, measured it, fab'd an identical one and started filing down the diaphram-end a smidgen at a time until I had a 1-second squirt, BUT with the rod not topped out in the dogleg "oval". This resulted in the throttle about 1/4 open before it started pumping, unlike the fork-pinch.
My theory is this may improve throttle response as when you first crack the gas on typically the intake velocity drops drastically, but by the time you're halfway into the throttle the revs are coming up and now the engine needs that fuel. I'll post on my site whether my butt can tell any difference after this weekend.
Just FYI my stock pushrod was 49.15mm and the final length I came to for proper squirt was 48.5mm. Yes, right now I have too much time on my hands... after the carb work I rebuilt my Specialized FSR Fox shock just because the shop told me it couldn't be done. ;)
I gave some thought to Anssi's point about the "delay", i.e. the A/P doesn't start to squirt until you've already got the throttle open some. Sooo, I pulled my carb, UN-pinched the fork and pulled out the A/P pushrod, measured it, fab'd an identical one and started filing down the diaphram-end a smidgen at a time until I had a 1-second squirt, BUT with the rod not topped out in the dogleg "oval". This resulted in the throttle about 1/4 open before it started pumping, unlike the fork-pinch.
My theory is this may improve throttle response as when you first crack the gas on typically the intake velocity drops drastically, but by the time you're halfway into the throttle the revs are coming up and now the engine needs that fuel. I'll post on my site whether my butt can tell any difference after this weekend.
Just FYI my stock pushrod was 49.15mm and the final length I came to for proper squirt was 48.5mm. Yes, right now I have too much time on my hands... after the carb work I rebuilt my Specialized FSR Fox shock just because the shop told me it couldn't be done. ;)
Guys-
This string is pretty old and buried, but if anyone's still watching it I need to update what I added last week about the "delay" on the AP.
Let's just say I UNDID the changes. After a day of technical hilllclimbs at Carnegie I must've stalled the bike a dozen times. Every time I'd get to a situation where I could lug the bike and let it just chug-chug before, now it had no torque. I'd either flail at the clutch and get the motor spun back up or it'd stall :think . It didn't help that I had a brand-new rear tire on either. I hope to get some time back out there tomorrow morning before the projected rain starts.:whiner:
This string is pretty old and buried, but if anyone's still watching it I need to update what I added last week about the "delay" on the AP.
Let's just say I UNDID the changes. After a day of technical hilllclimbs at Carnegie I must've stalled the bike a dozen times. Every time I'd get to a situation where I could lug the bike and let it just chug-chug before, now it had no torque. I'd either flail at the clutch and get the motor spun back up or it'd stall :think . It didn't help that I had a brand-new rear tire on either. I hope to get some time back out there tomorrow morning before the projected rain starts.:whiner:
Strick
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What? Please explain. Are you still running the stock pilot and the E MN? That needle has never treated me well. I had the same low end stumble no matter what I tried.
When was your last valve adjustment?
Is your crankcase breather rerouted? How's the carb plug holding out?
When was your last valve adjustment?
Is your crankcase breather rerouted? How's the carb plug holding out?
Strick-
The bike didn't "stumble", it just wouldn't make any damn power down low. When it was right I could lug it pretty low in the revs in second (14/50 sprockets) and the motor would just hunker down and the power pulses would become nice, crisp punches forward with the exhaust note slowing to a distinct series of pow-pow-pows in my right ear. After the a/p change I mentioned (setting a delay) the revs would drop down below the midrange and just get all mushy, no more torque. So I'd flog the clutch and WAAAAA the thing would take off again. Unfortunately during that a/p modification I also raised my float level from 10 to 11 mm in an effort to quell the overflow, hoping to help my fuel efficiency, and of course I changed THAT back too, so I won't know whether it was the a/p or the float level that messed up my bottom end. My most important priority when I go riding for the day is that I can RIDE for the day, and mess with it again afterwords. I have little interest in tearing off my carb in the dusty, windy creekbed at Carnegie while I try different settings, though it really is the ONLY way to see what works; back to back.
I'm gonna start hassling Bob (Old Stroker) for the needles he's raving about now. He called me last week to tell me I won't WANT a 454 kit after I try his new magic needle-of-the-week. I'll believe it when I ride it.;)
The bike didn't "stumble", it just wouldn't make any damn power down low. When it was right I could lug it pretty low in the revs in second (14/50 sprockets) and the motor would just hunker down and the power pulses would become nice, crisp punches forward with the exhaust note slowing to a distinct series of pow-pow-pows in my right ear. After the a/p change I mentioned (setting a delay) the revs would drop down below the midrange and just get all mushy, no more torque. So I'd flog the clutch and WAAAAA the thing would take off again. Unfortunately during that a/p modification I also raised my float level from 10 to 11 mm in an effort to quell the overflow, hoping to help my fuel efficiency, and of course I changed THAT back too, so I won't know whether it was the a/p or the float level that messed up my bottom end. My most important priority when I go riding for the day is that I can RIDE for the day, and mess with it again afterwords. I have little interest in tearing off my carb in the dusty, windy creekbed at Carnegie while I try different settings, though it really is the ONLY way to see what works; back to back.
I'm gonna start hassling Bob (Old Stroker) for the needles he's raving about now. He called me last week to tell me I won't WANT a 454 kit after I try his new magic needle-of-the-week. I'll believe it when I ride it.;)
What, was it YOUR new magic needle?
Look, no matter WHAT needle somebody puts in their bike SOMEBODY'S gonna find a better one. I'm running an EMN#5 and I'm not so impressed with it. Perhaps my bike needs an exhaust or something, or maybe I should'a could'a would'a bought a 520, point is it could always be faster, but I could always lose 10 lbs and not be such a chickensh!t either!!! :D
Keep it comin!!!
Look, no matter WHAT needle somebody puts in their bike SOMEBODY'S gonna find a better one. I'm running an EMN#5 and I'm not so impressed with it. Perhaps my bike needs an exhaust or something, or maybe I should'a could'a would'a bought a 520, point is it could always be faster, but I could always lose 10 lbs and not be such a chickensh!t either!!! :D
Keep it comin!!!
Strick
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You and I must ride and think alike! I will shoot you a PM on my best set-up discovery - so far. I also bought an extra airbox cover that I am drilling out to see what increased air flow does. I just love to experiment. Actually I have ridden one bike (400SX) with an open airbox and was impressed. A local A racer has the airbox opened up on his 520exc, and it dyno'd 2hp higher than stock.
Good LucK and I will post back my airbox results.
OLD STROKER
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- Feb 19, 2001
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I always say, give credit where credit is due. Strick originally brought up this needle on another board:( He said it came from one of those guys in blue. Strick, you ought to get him on this site so he can share some of his findings. I don't know if you have been looking at that other board, but to fill you in I've tried the followind D.. needles. DMM, DMN, DMP, DMR and DMS. I had great sucess with the DMR and DMS, but when I tried the DMN (it was on B/O) it became the needle of choice. My settings were....
172 Main
48 Pilot
DMN Needle #4 clip
1 1/2 turns F/S
P-38 1 sec. squirt
This coming weekend I'm going to jump to the extreme and try a 180 main jet and then go from there. It seems the richer you get these bikes the better they want to run.
Bob
172 Main
48 Pilot
DMN Needle #4 clip
1 1/2 turns F/S
P-38 1 sec. squirt
This coming weekend I'm going to jump to the extreme and try a 180 main jet and then go from there. It seems the richer you get these bikes the better they want to run.
Bob
