stroker problems

[trx250r180]

im trying to help someone that bought one of my old 250r quads,i had it setup as a 89 crank 86 piston with spacer plate,he had idea to buy a stroker kit crank off ebay ,keeps the spacer plate and now has a 89 piston ,is also a 89 cyl,the thing has no bottom end throttle response now ,will rev out and starts first kick easy but been all over with jetting ,and i hae him back where we started 35 pwk air stryker 48 pilot cek needle and 158 main,is the port timing way off now ? or am i missing something else to make run good,it ran fine before ,im trying to talk him into an 89 crank 86 piston again ,anybody ever have this problem???

[zedicus00]

dont just add a stroker crank to something with out having it reported or it definatly wont run right. iether go back to the non-stroker crank or hav it reported. you could get a different thickness spacer plate and then hav the dome cut and that would help but to be right it should still be reported even if using a thin plate with the head mod.

[wilkin250r]

It's a port-timing issue.

Think about HOW the timing is set. It depends on the piston and crank, and the stroker changes the angles and distances of the crank. Therefore, the stroker changes the port timings.

Without any other modifications, you get a motor that SHOULD rev slower because of the increased stroke, but instead wants to rev faster because of the port timing.

If the cylinder has been ported, he may need a new one. If it hasn't been ported, then it needs to be ported for a stroker, and head mods to go with it.

Either way, it's not something you or him can do yourselves. That motor needs professional help.

[deathman53]

Correct me if I'm wrong, but I saw a very simialr situation. 250r motor with a long rod, long rod piston and spacer plate, did the same thing. We kept the head off and put the motor through a cycle, there was a gap of where the head goes and the piston, unlike how the piston should be nearly to the edge of the cylinder. We took off the spacer plate and it ran alot better, maybe you need a different thickness spacer plate for the stroker crank and you definetly need the cylinder re-ported for the stroker crank. Contact c-leigh on this site, he builds 250r motors and can shed some light on this motors setup better.

[redrooster310r]

the plate changes the port timing

[kiesta00]

Originally posted by deathman53
Correct me if I'm wrong, but I saw a very simialr situation. 250r motor with a long rod, long rod piston and spacer plate, did the same thing. We kept the head off and put the motor through a cycle, there was a gap of where the head goes and the piston, unlike how the piston should be nearly to the edge of the cylinder. We took off the spacer plate and it ran alot better, maybe you need a different thickness spacer plate for the stroker crank and you definetly need the cylinder re-ported for the stroker crank. Contact c-leigh on this site, he builds 250r motors and can shed some light on this motors setup better.

You don't run the spacer plate with the long rod crank and long rod piston, you only need the spacer plate with the 86 style piston being used. Depending on the stroke, the 87-89 style piston skirt needs to be milled so the piston doesn't hit the crank when at BDC. Just be carefull when setting up motors with spacer plates and porting, you don't want the exhaust to freeport just to get the correct deck height/port timing. Talk to someone who has experience with stroker 250r motors to do your engine work.

[trx250r180]

thanks for input guys,im gonna tell him to buy a 89 crank and 86 piston like i had it set up with the plate or 89 crank and piston and no spacer if he wants to use his new piston,and tell him lesson learned ,bigger is not always better,i had an issue with an old mickey thompson engine 89 top with yz piston,flat off bottom then would rip your arms off,ended up putting reg 89 cylinder back on,ive had 250rs for 15 years or so and never messed with stroker rods so i was kinda lost for ideas on making run right

[kiesta00]

the added stroke comes from the crank, not from the longer rod. just lettin ya know ;)

[86 Quad R]

as mentioned. the problem is port timing. the cylinder needs to be setup for the added stroke of the crank but, doing so with an already ported cylinder can be sketchy(hit and miss). ideally you'd want to start with a "virgin" cylinder due to the fact that the roof and floor of an already ported cylinder may have been carried beyond that what is required for making a stroker setup do its job efficiently. once setup right the engine will deliver great torque and power.


as keist mentioned about using the 87-89 piston combo on a stroker you'll definately need to mill the skirts down to clear. i like this combo because it allows you to run without a spacer plate and therefor doesnt decrease crankcase pressure which is what makes the 250r what it is to begin with.

[kiesta00]

Originally posted by 86 Quad R
i like this combo because it allows you to run without a spacer plate and therefor doesnt decrease crankcase pressure which is what makes the 250r what it is to begin with.


How does decreasing crankcase pressure affect the motor? less force to move the air/fuel mixture into the cylinder?

[deathman53]

the reason for a spacer plate and how it affects crankcase pressure and volume is simple. The more crankcase pressure the more "hit" it has, it is more noticable and at times less controllable and tires you out faster. People use the spacer plate setup to reduce pressure and increase volume, what it does is make slower hitting, but less tiring and more controlable power, basically, less wheel spin and more hook-up. Reed spacers do the same thing, more crankcase volume, making more tractable power. It is argued wether reed spacers do anything, though.

[86 Quad R]

on a small cc engine you can notice the difference of having a reed spacer or not. same with a base plate.

[kiesta00]

good to know, I have a spacer plate and mine still hits perdy hard lol