A forum for owners of Yamaha TTR250 trail and enduro bikes!

TTRMike · Veteran Member

Later Model Carb Mods

TTRfan · Super Guru

Thanks for the info Mike. I think this forum has attracted a lot of new TTR owners who may not have used the old Yahoo one. Any chance you might paste up your item here please with any updates needed? Cheeky question as you are busy preparing for the Cambrian but no rush wink

Brian

Lin · Senior Member

We are going to be fitting FMF pipes to our 2010 TTRs. Mike any advise you can offer would be appreciated.

TTRMike · Veteran Member

Will Have a look and see if I can find it Brian ... ha confuse !

Which pipe are you going for Lin? I have just fitted a Q4 to my 2004 bike and its made a significant difference to the performance. Having said that, I have decorked the standard header pipe. I've not made any mods to the air box or filter as I spend far to much of my riding time in wet and boggy conditions so I'm reluctand to remove snorkel or drill holes in the box. As far as jetting is concerned I have a 50 pilot jet and a 145 main but this is in a 1998 model needle jet, which has a shorter hex than the later/blue models. Of course, if you do need to alter the needle jet you will have to adjust the float accordingly. I'll try and find the Yahoo article that I posted and this may shed more light on the matter. I'll also post up some pics of the two needle jets when I have 5 minutes so you can see the difference. I have set my mixture screw at one and three-quater turns from fully in. You can get FMF recommendations here; http://ridersupport.fmfracing.com/JettingCenter

Hope this gets you somewhere near

TTRMike · Veteran Member

Found it Brian wink !

The linked article describes my successful experiment to resolve the overheating and and poor performance of my 2004 standard TTR; http://www.ttr250.com/carb_fix.htm

I have since found that the plastic baffle in the 2004 float bowl was also in the OE carbs but beware, the baffles are not the same. The 2004 baffle can be carefully modified but you would need an ealier one to compare it with. I have left it out altogether!

domski1 · Senior Member

TTRMike wrote:
Will Have a look and see if I can find it Brian ... ha!
Which pipe are you going for Lin? I have just fitted a Q4 to my 2004 bike and its made a significant difference to the performance. Having said that, I have decorked the standard header pipe. I've not made any mods to the air box or filter as I spend far to much of my riding time in wet and boggy conditions so I'm reluctand to remove snorkel or drill holes in the box. As far as jetting is concerned I have a 50 pilot jet and a 145 main but this is in a 1998 model needle jet, which has a shorter hex than the later/blue models. Of course, if you do need to alter the needle jet you will have to adjust the float accordingly. I'll try and find the Yahoo article that I posted and this may shed more light on the matter. I'll also post up some pics of the two needle jets when I have 5 minutes so you can see the difference. I have set my mixture screw at one and three-quater turns from fully in. You can get FMF recommendations here; http://ridersupport.fmfracing.com/JettingCenter
Hope this gets you somewhere near

I have been thinking about buying a fmf q4, how quiet are they compared to the standard system and where is the best place to buy them from in the uk? I gave seen them on eBay from America but not found any uk based. Cheers Adam.

TTRMike · Veteran Member

The Q4 is quite a lot louder than the standard pipe but I don't think its offensive Adam. Its probably a tad louder than my TTR600 on the standard pipe. You can get Db reducers if your pipe is too loud but I'm not sure if you can get one for the Q4. I don't know of anywhere in the UK doing them now. If you decide to order from the US you will need to add around £40 to the price as you will get an import charge. I think its still a cempetative price though. They usually say 15 days from dispatch to delivery but this can vary dependant on customs etc. Three weeks is probably more realistic.

TTRMike · Veteran Member

Whilst I think about it Adam, if you do go down the route of an FMF pipe, I'd think twice about buying a jetting kit from ebay. Kits are said to be 'tailored' to suit your set up. To be honest I wasn't impressed when I tried the kit out of curiosity. You get 3 main jets which are an alternative make to standard, a couple of needle shims some instructions that are what I would consider to be general tuning knowledge, a wood screw and a 3/8 drill.

Your unlikely to require needle shims as this is very critical tuning.

You can go to your local Yam dealer and order a couple of jets either side of your standard jet and they are correct fitting.

You can can get the general knowledge from the leared folk on the forum for free.

As for the wood screw and drill ... wood screws are for wood and its never a good idea to be waving drills at carbs for any reason!

-- Edited by TTRMike on Saturday 1st of October 2011 11:24:43 AM

-- Edited by TTRMike on Saturday 1st of October 2011 11:27:58 AM

Lin · Senior Member

TTRMike wrote:
Will Have a look and see if I can find it Brian ... ha!
Which pipe are you going for Lin? I have just fitted a Q4 to my 2004 bike and its made a significant difference to the performance. Having said that, I have decorked the standard header pipe. I've not made any mods to the air box or filter as I spend far to much of my riding time in wet and boggy conditions so I'm reluctand to remove snorkel or drill holes in the box. As far as jetting is concerned I have a 50 pilot jet and a 145 main but this is in a 1998 model needle jet, which has a shorter hex than the later/blue models. Of course, if you do need to alter the needle jet you will have to adjust the float accordingly. I'll try and find the Yahoo article that I posted and this may shed more light on the matter. I'll also post up some pics of the two needle jets when I have 5 minutes so you can see the difference. I have set my mixture screw at one and three-quater turns from fully in. You can get FMF recommendations here; http://ridersupport.fmfracing.com/JettingCenter
Hope this gets you somewhere near

We are buying the FMF Powercore. According to the FMF website we will be ok with standard jetting. The primary pipe is already changed to the short one Brian sells and it provided a noticeable mid-range torque increase. We have 52 pilot jets (changed from the standard 50) and 140 mains. Needle up one notch. I have a couple of earlier needle jets but didn't fit them, as far as I could see they are just a bit shorter. All the drillings look to be the same as the later version, but of course the eye is not enough to pick up fractional dimensional variation to the emulsion holes etc. We are operating in high ambient temperatures and I don't think the 52 pilots gave any benefit, I may just go back to 50s.

Most of our original tuning issues evaporated with the removal of the primary pipe baffle.

The Yamaha dealer lists the alternative 52 pilot jet but no alternative 145 main jet. Where did you source your 145? I know Teikei jets are flow sized whereas Mikuni are graduated according to hole diameter so there is no direct interchange here despite what some web postings say.

TTRMike · Veteran Member

You have to wonder what goes on that there are all these variants and some work but some don't Lin. As you say, as far as I can tell the only difference in the needle jet is about 3mm length on the hex. It would be interesting to try running my bike on the shorter header to see if this makes any difference to carburation on mine??? My best result was the 3rd notch on the needle. I still have a major question over why the longer hex results in the need for a larger main.

The procedure I described turned out to be the simplest, most straight forward option to resolve the overheating issues that some experience but once you get into after market pipes, filters and so on your into new teritory. I suppose various combinations will work with a little bit of know how.

I'm surprised you can't get the 145 main from dealer. What a pain. I sourced mine from endless 'junk until you need it' boxes! If I find a source I'll post it up asap. It may be worth you trying jets from the kits on ebay. If you want to try them I can throw a 145 in post to save you shelling out for an unknown. I won't be using it.

Lin · Senior Member

Thanks for the offer of a main jet, if I think we are going to need it I'll let you know. Just curious to learn that your Yamaha dealer could supply whereas mine cannot find a part number for it.

I have access to a selection of jet drills and already tried a slightly enlarged main while still on the bog standard exhaust. The bikes actually ran much worst on the larger main. This was when we were battling performance issues that were magically resolved by removing the primary pipe baffle. However, as you say with an aftermarket pipe we enter new territory.

I have a fair suspicion our bikes are tending to be a bit on the rich side with stock jetting. We are operating in the Philippines in ambient temps mostly +30degC and more, so the air density is lower. Possibly that's why they responded so well to snorkel removal and airbox mods.

To compound the matter Philippine fuel has different characteristics UK/AUS/NZ fuel. The baffle removal allowed the engines to exploit the full rpm range, before removal they would surge, miss and refuse to run past half throttle. I suspect the restricted pipe was "poisoning" the combustion because too much Philippine-fuel exhaust gas was still trapped in the cylinder. The fuel is pretty awful stuff - one can pour it out into a dish and it will just sit there all day without evaporating....

Concerning the shorter/longer needle jet, I have not come across any information that changing a needle jet from short to long or vise versa resolved any issue. My only thought is that a longer one may have been produced to overcome potential starvation due to fuel slosh during violent direction changes. Or maybe Teikei installed new production machinery that made the part 3mm longer.....

TTRMike · Veteran Member

Very different conditions to the Uk then Lin. Re baffle removal, the issues here are near identical even with uk fuel. As you say, way too much back pessure. I did at one point work out the % of how much the pipe was reduced by. The figures were rediculous. Pre removing it, I couldn't hold top gear on the flat! I'm not sure about the jet length thing. I had assumed it was to do with a gaff attempt at reducing the emissions. I'm pretty sure that the plastic baffle in the bowl is to stop the sloshing issue. I did try contacting Yam UK at one point but they were no more the wiser than you or I. Really interesting to hear about your problems though.
Just out of interest, I had similar problems with jetting on my 2002 XT600 and that was all about emision controls, and that was delivered to me with 2 miles on the clock.

Lin · Senior Member

I'd be fairly confident in saying the primary pipe baffle is intended to be a cheap form of exhaust gas recirculation (EGR) system. High combustion temps from larger throttle openings increase Nitrogen oxide (NOx) in the exhaust gas, combustion temp can be lowered by retaining a percentage of exhaust gas in the cylinder. Sort of a basic EGR valve - this strategy is employed by a number of motorcycle manufacturers. It's pretty crude and without any form of modulation so it's not surprising drivability issues arise.

Pre baffle removal we tried different brands of fuel and found some improvement depending on brand. Really had us scratching our heads. Baffle removed and all the problems went with it. Took three days out of my life trying figure the damn thing out as we didn't know there was a baffle in there.

The plastic baffle in the carb as you say is a fuel slosh baffle for sure, seen it in many carbs, both automotive and motorcycle. The longer needle jet is a mystery to me, I'd like to take take a long and short one to a lab and get a comparative dimensioning done.