Hard starting with Mikunis

[philrock]

Last Saturday I ran my Hartman with dual Mc101s at the Santa Maria track. The 101s have 34 mm Mikuni pumper carbs on them (one carb per engine). The engines/carbs ran really great - after I finally got them started - it took forever to get the carb pumps pumping. I had to go to a lot of trouble filling the gas lines, priming with carb cleaner, and doubling up on starter batteries (to get the cranking speed up). The diaphragms and metal parts are in excellent condition. Popoff pressure and fulcrum arm heights are correct. Tillotsons and Walbros have never given me this kind of grief. Any ideas on what might be causing this problem?

[Rob Voska]

Did you choke it by hand cutting off all the air (no air cleaner) so it had to pull fuel?

Were the inlet needles gummed up / stuck with dry gas / oil from the last time you ran it?

Are you sure your pulse holes are 100% aligned & clear?

What do you flush your engines with?

Are you running gas or alky?

Are your reeds in perfect shape and seal well?

[ted johnson]

I run Mikunis almost exclusively, though usually on alky. I even run a floor pan mounted tank. I never have any issue with them but one: If you run a Viton-tipped inlet needle, they DO have a tendency to stick closed. I have had to remove the pump stack and free the needle more than once. Once that's done, I run the rest of the weekend with no troubles. The second question is do you have a completely free pulse path. I run an external pulse on the alky carbs. TJ

[steve miller]

TJ .. i was gonna ask about the needle .i cant seem to run anything but solid brass or whatever they are made off .the ones with tiny rubber tip and the plastic ones stick all the time on me ..i use maxum 927 caster its easy for me get and it will blend with gas or meth .But it will gum up in a carb in a week then other times there fine ? ..on small carbs like flat backs i hogged out a stock mcculloch intake and put in pyramid reeds .and the pulse hole is tiny i mean tiny like not much bigger than a sewing needle it pumps fine ..ive tore motors apart with gasket goop almost covering the hole,broke rings and they still pump its amaizing what you find sometimes ..

[philrock]

Hello guys. Thanks for your thoughts and questions.

I choked it with no air cleaner and the intake pretty well sealed. Last Saturday this did not force it to pump. When I did the same thing a couple of weeks ago at home, it pumped like a fire engine.

Last Saturday, after cranking until the starter battery almost gave up, I checked the spark plug, expecting to find it drenched in fuel. It was dry as a bone.

I don't know the material or current condition of the inlet needles - I'll check.

Pulse holes are not lined up perfectly, but they'll easily pass a 1/16" drill bit. Since the engines run great once started, doesn't that mean the pulse passages are good enough?

I run 91 octane pump gas and Blendzall 460 (or Burris Hi-Rev Red Label), 16:1. Since I'm running gas, I don't flush. I know this is a pretty rich mix, but I'm not making too much smoke, and the sparks plugs are a perfect tan color.

Of the 8 reed petals in the two engines, 2 have very small nicks in the tips. The nicks are nowhere near big enough to allow a leak. The reeds appear to be sitting down properly against the pyramids, but I can't be sure they're sealing well - especially at the low speeds and pressures involved in starting.

[Rob Voska]

Lift off the pumper plates & push fulcrum arm down. I'll almost guarantee the inlet needle is "stuck".

[ted johnson]

I've gotten to the point where I just unscrew the stack before I run, and free the inlet needle. Once it's freed, it'll usually stay free for the weekend's running. If you can't get hold of it with your fingernails, you can free it with a popoff tester. I always keep tweezers in my tool kit. TJ

[steveohara]

No need to remove the plates.... just pull the fuel line and connect your pop off gauge and pump it up until it blows air through. If the pop off gauge shows a much higher reading the first time then the needle was stuck and you should bleed off all the pressure and test again to see if you get your normal read on the pop off pressure. If it doesn't act right, fill a few inches of the pop off gauge line with clean fuel and do the test again and keep pumping until you push the fresh fuel all the way through to the throttle bore.
Once you push the clean fuel through, re check and you should get a proper read on the pop off.
Steve O'Hara

[ted johnson]

Steve's right. The last time it happened to me, I didn't have a popoff tester in the travelling toolbox. That's why we removed the stack. The Mikuni needles are the only ones I ever have issues with. We'll see if the problem continues now I've switched back to gas.

[steve miller]

phil .this is only a suggestion but if it happens again id think about turning the motor over that many times DRY .. if you ran a 12 volt battery dead id say that motor turned over a few hundred times dry as a bone good thing you running so rich prolly lotta build up in crank case ..if any of my motors wont start in 3 or 4 pulls or very few spins with electric i at least dump fuel in carb and fire it of if it wont stay running then you no you got problems ..just a thought ..