Jump to content
Sign in to follow this  

Jetting Question '98 XR400

Recommended Posts

Hey all, this is my first post here. First let me thank everyone who has put so much time into these pages. What great information. So I have searched and searched these pages and gotten a lot of information, but I'm still struggling jetting my 1998 XR400 so I figured I would finally break down and post my problem.

My bike was jetted perfectly for 7000 ft in Colorado. It was running

116 Needle in third position

52 Pilot

145 main.

The snorkle is removed and it is running an FMF pipe. It started fairly well but once it was warm it started like a dream and ran like a top.

I recently moved back down to sea level (350 to 500 ft. actually) and my bike (of course) didn't run well. I richened the mix by putting in a 162 main as the FMF and various other areas suggested. So anyway here is the issue. The bike now acts like it is running leaner than before. This is strange right? or am I just too much a jetting newbie? The bike would idle well after a lot of kicks and warm up but bogged at higher RPM's. After a few trips out I pulled the new plug and it was powder white which I understand is a sign of leanness as well. I just pulled the carb and there was a bit of grit in the pilot jet, but I assumed this would more effect off idle and not higher running. It wasn't much grit and like I said it was idling decently, not like before though.

I just adjusted the valves and there was no real appreciable adjustment. Just a bit tighter on all four. The compression release is disconnected and the actuator wired back so it cannot engage. I pulled the valve cover off and everythign seems to be in good working order.

I looked over the shop manual and it does not say how to adjust the timing. It just states to check the timing and assure it is right, so I'm not sure what to do there. Is it just right or you're replacing ignition parts?

At any rate, any advice anyone has would be great. The thing won't even start now. I have not had a chance to give it a kick to see if it does any better with the pilot cleaned and the valves adjusted.

Could this all have just been caused by a dirty pilot jet?

This is the Keihin carb (I'm not sure if there is a variation there or if all XR's in 98 ran this carb.

Share this post


Link to post
Share on other sites

As I keep searching I realize that people are recommending a 60 or 62 pilot with a 162 main. So is my pilot being this lean (52) be the culprit?

Share this post


Link to post
Share on other sites

I know it's a hassle changing the pilot, but you can't go from 7k to sea level and not change it. Yes, the lean pilot would have an effect on starting at sea level, as it has everything to do with the starting circuit, it and the fuel screw. Experiment with a 58 and a 60 pilot.

I think the 162 main may be too rich. Experiment with a 158 and a 160.

The timing isn't adjustable. You problem doesn't sound ignition related.

I would be sure you adjusted the valves right, on the right stroke at TDC and didn't make them too tight. To err on the loose side of the spec is better. Too tight valves will make for hard starting.

Share this post


Link to post
Share on other sites
I know it's a hassle changing the pilot, but you can't go from 7k to sea level and not change it. Yes, the lean pilot would have an effect on starting at sea level, as it has everything to do with the starting circuit, it and the fuel screw. Experiment with a 58 and a 60 pilot.

I think the 162 main may be too rich. Experiment with a 158 and a 160.

The timing isn't adjustable. You problem doesn't sound ignition related.

I would be sure you adjusted the valves right, on the right stroke at TDC and didn't make them too tight. To err on the loose side of the spec is better. Too tight valves will make for hard starting.

Thanks man! I appreciate the response a LOT. Yeah, the valves were done right, just like you said, right in the middle to a bit loose on the speck.

This is a good lesson for me listening to the guy at the local shop. When I was searching for jets I asked him about pilot jetting and he said it didn't matter as long as the bike was idling. Oh well, at least I finally got the thing sorted out. I'll get myself a 58/60/ and 160 main and futz around.

I am finally learning about carbs! Woo Hoo!

Thanks again!

Share this post


Link to post
Share on other sites

Ok well this is a fairly simple question.Does jd jetting make a jetting kit for the mikuni pumper.and do i need specific jets for this carb or are they universial like most on stock carbs?I am

Share this post


Link to post
Share on other sites

I don't know if JD makes a kit for the Mikuni pumper. Most times all a kit is is a main, pilot and sometimes a different needle. And not necessarily the optimum setup for what "your" specific conditions are.

I think "kits" are for those that don't have a clue as to how to tune their carb, don't know any better and assume a kit is the answer to their woes.

The Mikuni jets are nothing special, just regular Mikuni jets. I forget the series numbers for the TM36. What Mikuni are you talking about? "This carb" isn't enough info.

http://www.sudco.com/mikunijets.html

If you're talking about the TM36-50 from XRs Only, it takes 130 main/15 pilot for elevations of about 6k and below. Above 6k you'd use a 125/12.5 combo.

Ok well this is a fairly simple question.Does jd jetting make a jetting kit for the mikuni pumper.and do i need specific jets for this carb or are they universal like most on stock carbs?I am

Share this post


Link to post
Share on other sites

JD includes 2 neddles about 4 mains and setting specs. There neddles have three tappers, where as standard have 2.

And they don't do one for the XR." Correct me if I'm wrong"

Share this post


Link to post
Share on other sites

Ok thanks all for the info.And for the record i have done alll the gordons mods and am running a uni filter.I have a fairly good idea what to run jetting wise as far as a base point.I run from sea level to say 9000 feet elevation and need to clean up the pilot jetting but am sure it will throw off the rest so was thinking rather them buy 1 or 2 single jets i could hopefully just get a kit and be able to dial it in......Robert (oh and it is the tm36-50 mikiuni)

Share this post


Link to post
Share on other sites

I don't think you're gonna get it done. Oh sure, it will run, but with that range in elevation you're always going to be either too lean or too rich, trying to get by with 1 jetting setup. It depends on how finicky you are with how your bike is running I guess.

Me, when I go up in elevation above what I have it optimally jetted for now, I rejet. I absolutely hate blubbering, poor throttle response, hesitation, lack of power and all that.

I run from sea level to say 9000 feet elevation and need to clean up the pilot jetting but am sure it will throw off the rest so was thinking rather them buy 1 or 2 single jets i could hopefully just get a kit and be able to dial it in......Robert (oh and it is the tm36-50 mikiuni)

Share this post


Link to post
Share on other sites

If I were you, I would get a second (used) carb and have one each set up for your favorite trails (elevations). A lot of xr riders have the Mukuni pumpers and sell the stockers on ebay for about $100. A lot simpler changeing carbs then jets and no risk of contamination by opening your carb.

Share this post


Link to post
Share on other sites

Hi all I've just ordered the Mikuni TM36 to relace the stock BS36 Mikuni that came with my 2009/10 DR-Z 400S.

I used the standard JD jetting kit and 3x3 mod and my bike runs well.

My Q is, do I need to rejet the TM36 or leave it stock standard to run with the 3x3 mod?

Also I have the stock pipe and plan to get a new one soonish. Any recommendations generally on making this change?

Any advice/help is always appreciated.

Cheers

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  

×