Hello, I’m new to the forum bit I figured this is the best place to ask a few questions.

I’m currently in the midst of my first build. There’s a few issues I need to get over.

I’ve deleted the airbox and replaced with a cone filter. Will I require re-jetting? Does anyone know the correct jet sizes?

My bike has the rubber covered footpegs- I’d rather have spiked metal ones. Does anyone know of alternatives?

Thanks!

from the UK.

Others will chime in soon with answers.

I think it'll probably be ok as it is but spray a little oil on the filter to catch the dust. Those little cone filters might be more restrictive than the original airbox. Trial & error [hope no error] Bottom line if ya worried then lift the needle a notch [that's move the clip down--if its in the center notch then go to notch 4 counting from the top. Then go up--guessing--10% on the main. That's all just to be safe, but think you'll end up back at original setting in the end. Other thing is i suppose if the filter is restrictive then you might need to reduce the main jet size & leave slide needle clip in the standard position. Sorry, that was no help was it. Welcome too.

Any reason for deleting the airbox? If it's for style points it would be better to try and get it going in stock form and then just change one thing at a time.

Yes guilty, it is for style points! It was/is running fine, the only two things I’ve changed engine wise is removing the oil pump/reservoir and airbox. I don’t mind premixing and I really hate the airbox. There is likely to be drastically increased air flow with a cone filter so I’m assuming main jet +4 and pilot +1. Needle not sure, maybe up one clip. Last time I re-jetted my crf250 I ruined it and created lasting problems though, so I might just get the local bike garage to do it...

Thanks for responding!

Hopefully you've removed the pump driveshaft and installed a block off plate for the pump? The shaft coming out of the case gets its oil from the pump... can seize up over time.

Just a note... those little K&N look-alike "hard cap" cone filters ... usually with a chrome end cap...can wreak havoc on jetting... there's a lot of pressure wave dynamics going on with a two stroke and the short length and hard end cap can result in intake resonance that makes it impossible to jet the carb.

If you get into a situation where the engine becomes rich or lean in a certain rpm range, switch to a foam filter. The problem is if you lean out the jetting to get rid of the richness, often it will be too lean at another rpm. Or if you richen to get rid of a lean spot, it becomes to rich somewhere else. Becomes impossible to jet. And the leaness can be bad enough to seize the engine.

I recommend using an all-foam filter to jet with... get it running good... then swap to your "looks" filter (which most, by the way, don't filter well and may end up drastically shortening engine life). Might need further small adjustments in jetting but if it suddenly goes rich... usually happens at mid-rpm range... resist the urge to lean it out because if you do, the engine will be lean above and below that rpm range.

Hi Mark,

Thanks for useful info. Is it really that hard to jet for a hard-cap filter? I’ve heard it’s not the easiest tune but I’ve never heard it’s ‘almost impossible’. To be very clear I’m not racing this bike, or even putting many miles on it. Probably <300/year. I’d like to think it is possible to have it running well with a cone filter?!

Sure, you could be okay. Just be careful about jetting to get rid of "rich spots" and making sure you don't have "lean spots"... both related to RPM.

Carb jetting is mostly about throttle position... not RPM... that's the key. Example: If it runs cleanly held at a certain throttle setting at lower RPM and at higher RPM but goes rich in between, then if you lean it out to get rid of the mid-range RPM richness it will be lean everywhere else.

There's different techniques to jetting... the Mikuni manual outlines theirs.

Hey Mark when you say you should remove the pump drive shaft are talking about part #3 in diagram
www.partzilla.com/catalog/yamaha/motorcy...1976/dt175c/oil-pump

Yes, that's it. Note seal (#6) is on the inside of the cover and bushing (#5) is on the outside so shaft/bushing will run dry if pump is removed and shaft is left in place.

(Shaft/bushing is lubed by premix oil from the pump)

If shaft seizes... plastic gear inside will strip/break. May or may not cause problems with debris floating in trans. Worst is if gear breaks and hardened pin #4 gets sucked through some gears... usually teeth strip before gear breaks though..