Help Mikuni and Rocker Issues!!!

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brett066

Member
#1
#1
Hi guys. well you helped me out with picking a cam, and now i need help working some bugs out on my build. To start with here is my combo: 200 clone, billet rod and flywheel, Tim's "black mamba" cam and billet lifters w/ matching shorter pushrods,22cc head ported, milled .050 w/ stainless valves(27mm intake), and 26lb springs. Timing is advanced 8*, and a 22mm mikuni. First problem: I bought a set of 1.3 rockers and the raceseng bronze bushed guide plate, but the guide plate is about 2x as thick as the stock one. It raises my pivot shafts too high and my pushrods pop out! So in an attempt to correct this i clearanced the holes in the old plate to fit the 1/4" dia pushrods, but the 1.3 rochers are shrter and the holes in the old plate wont allow a change in the pushrod angle to accomodate this so for now im running the stock rockers. Can i thin the mounting side of the plate to get the geometry i need? Is this somethin a machine shop should handle or could i do this with a sander or file and a steady hand?Problem 2: With the mikuni, bike is extremely hard to start and bogs when i approach WOT. I understand that theese things take tuning on these motors, but i have never really messed with them. Would the difficult starts be the low speed circuit? And i assume the bogging down is due to the main jet? I realize there is no universal setup, but could someone give me a ballpark estimate on where to start as far as jetting? Would i just size up jets accordingly if i fix my guide plate issue and go from the stockers to the ratio rockers? I know i just posted a small novel on here and im sorry, but its getting frustrating spending all this time and money and not really being able to enjoy the bike.Thanks in advance for any help you guys can give!!
 
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Caseyslowgto

New Member
#2
#2
What rockers did you get? Stamped or shaft mounted?
Also when you mill the head don't you have to make up for the amount of material that has been removed(dunno not sure)?

What jets are you running in the Mikuni? You say it Boggs at WOT, is that the only point where you have this issue. Example my old Mikuni would bogg when you went WOT but if I slowly stepped into it she would seem fine(wasn't fine but lean).
 
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brett066

Member
#3
#3
They are the stamped rockers. I thought the milled head surface would kind of cancel out the thick guide plate to, but i think it might be because the rockers themselves are shorter from fulcrum to pushrod cup, and the bushings in the guide plate are free to slide back and forth the length of the slots in the plate. I thoght about peening them to make them stationary, but i dont wanna stick them in the wrong place and cause possible binding issues. As for the carb, i really dont know what # jets are in it at the moment, i know the jet needle is in the center slot, should i maybe move it to a richer setting? As for the wide open throttle deal, i can get it there by REALLY babying it, like im talking in a 2 block stretch i usually just make it to WOT when its time to start braking. THe main problem i would like to solve asap is the ridiculously difficult starts. I am thinking it is a carb issue, any ideas? Also, i have a pulse pump, but had a serious flooding problem(like almost steady stream of fuel out of the overflow line with a cuople heavy blips of the throttle) so i disconnected it and hooked it back up gravity feed. Dont know if that might help tell you something?:shrug:Thanks
 
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Caseyslowgto

New Member
#4
#4
Well I'm kinda stumped on what to do about the rockers. Either keep the RS guide plate and run stock rockers or the ratios with a modified stock guide plate I think. Contact Raceseng they might be able to help you on that one cause I run shaft mounted and don't need a guide plate so....

The Mikuni issue sounds like mine, I would go ahead and set it to the richest on the needle jet. If the carbs the same as mine was it should have a #15 pilot jet and I think they recommend changing to a #12.5. The main jet should be between 95-105 and I think most run in the 120-130 range. Now about the overflow the Mikunis prefer to be gravity feed, when I had mine on my kart with a pump it would blow fuel out of every hole at anywhere near WOT.

I don't know why it is hard to start
 
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collinsdad

New Member
#5
#5
with my carb there is no way it will rev up with a 12.5 pilot jet i use 17.5 or higher and cutting the head has nothing to do with your rocker arms,shim up the studs
 
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collinsdad

New Member
#6
#6
sorry i got ahead of myself with out fully reading your post,it could very well be the pushrods,as for hard starting,try giving it a little throttle and see if she starts easier,with my sons motor it will not start without a little throttle
 
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brett066

Member
#7
#7
Well I'm kinda stumped on what to do about the rockers. Either keep the RS guide plate and run stock rockers or the ratios with a modified stock guide plate I think. Contact Raceseng they might be able to help you on that one cause I run shaft mounted and don't need a guide plate so....

The Mikuni issue sounds like mine, I would go ahead and set it to the richest on the needle jet. If the carbs the same as mine was it should have a #15 pilot jet and I think they recommend changing to a #12.5. The main jet should be between 95-105 and I think most run in the 120-130 range. Now about the overflow the Mikunis prefer to be gravity feed, when I had mine on my kart with a pump it would blow fuel out of every hole at anywhere near WOT.

I don't know why it is hard to start
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Sweet! thanks dude. Answers a lot quicker than i expected. I guess i will do some jet changes and tuning and see if it gets any easier to start. Higher octane fuel maybe?? I mean i didnt actually set and figure my ratio, but i wouldnt have thought i had bumped it up to the point where its not pump friendly?? Anyway thanks again dude, been goin nuts with this the last couple of days:cursing:
 
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brett066

Member
#8
#8
oh yeah, i guess i left that off the list! It also has a flat-top and a +.010 rod. That plus milling .050 off and the stainless valves are a little flatter on the head than the sort of dished stock ones.What would your guess be as to what my compression is? Also using a stock style head gskt.
 
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brett066

Member
#11
#11
collinsdad said:
what do you mean you milled .50 off the valves????i have a 14cc head milled .065 and i run race fuel,im totally stumped with the milling of the valves
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Sorry, fast typing not my strong suit:doah: .050 off the head, and i meant the valves take up a little more room in the chamber than the stockers
 
Bikerscum

Bikerscum

Active Member
#16
#16
collinsdad said:
as for hard starting,try giving it a little throttle and see if she starts easier,with my sons motor it will not start without a little throttle
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+1

I have a Predator, milled head, Black Mamba cam, 22 Mikuni etc. etc. I give it one mighty pull with the choke on, then take the choke off & hold about 1/3 throttle. Gotta be real careful as she wants to take off when she starts. High stall springs on the TAV helped a lot with that.
 
Bikerscum

Bikerscum

Active Member
#18
#18
Caseyslowgto said:
My GX160 with a Mamba won't pull start at all. It doesn't spin the motor long and fast enough to get it started. I have to use a drill or starter.
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Does the cam have a compression release?

Mine was a beast to pull start at first, but it's getting easier. Finding the right technique is the key.
 
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