Technical carb question

[RIDE-RED 250r]

Well, I spent most of the day in the garage with my brother (Ride-Red-Man) working on his Bayou and Tri-Z he just got...

Long story short, we are trying to make one of my old Keihin PE34 on the Z. It's an easy fit no problems.

I'm having a bit of intermittant trouble with the bowl overflowing. It seems to only do it when spooling the engine up pretty good.

So, I get my Honda manual out to start checking float height specs for that carb, no problem right..

My question is this: Am I supposed to let the float arm tang compress the little spring loaded plunger on the fuel metering needle? Or do I hold the carb on it's side and take the measurement from the point that the needle just bottoms in the seat and the tang just begins to touch the little spring loaded plunger? The reason I ask is the book is a bit unclear on this and it makes a significant difference doing it one way vs the other.

The carb is squeaky clean, 100%.

I had a passing thought that being the Tri-Z utilizes a fuel pump rather than a top mount gravity fed fuel system that maybe the float height needs to be a touch taller??? I only had this thought since it only seems to overflow when spooling up the engine, which increases fuel pump volume and I would assume pressure. Is there any plausibility to that theory? Or should I just concentrate on figuring out the correct method for measuring float height and go from there??

Having fun getting to know the Tri-Z! I think the PE34 should be a descent upgrade for him.....I know there's better, but that's all I had kicking around right now....

[Flyingw]

First of all, you hold the carb to where the tab just barely touches the plunger........barely then measure the height.

The first ting to consider is gravity feed over pressure fed. Gravity feed fuel systems rely on air behind liquid for positive flow whereas a pressure fed system forces the liquid in to the bowl. As the bowl fills, it displaces air through the vent tubes always keeping the pressure in the bowl neutral. Now matter how the fuel flows in to the bowl, the float valve will cut it off according to the float height. The output of the Z fuel pump really isnt much more than gravity feed so that should nt be an issue just make sure the tank has a vent thats open.

[Jason125m]

x2, Hold the carb on its side so the needle is seated but the needle spring is not compressed at all. I just went through this, took me a while to figure it out..... too long actually.

[RIDE-RED 250r]

Thanks for the replies guys. That's what I was leaning toward and I needed a little confirmation.

[El Camexican]

Hang on Buddy! I just went through this with my Tri-Z. You can search the posts if you want, but the bottom line is that the fuel pump makes too much pressure for a carb that is designed for gravity feed fuel. I solved my problem by putting a restrictor in my line just past the return line, but most of the advice I got was to open up the 3/8" return line because it is actually restricted inside the tee (I have not actually looked at this) zmpolaristech seems to have a lot of experience with this and he recommends using a sled carb (fuel injection sled) but modifying a Keihin that did not come with this restrictor can't be done as the orifice is part of the carb body, you’d need to buy a whole carb and they don't make new ones. Others suggest the aluminum tee for sale in the 3WW store. I think that is the best option for your situation, but you can try my restrictor line if you want, just don't blame me if something melts.

http://www.3wheelerworld.com/showthread.php/143132-TRI-Z-Fuel-Pumps

[RIDE-RED 250r]

Thank you very much El Camexican!

That is EXACTLY the issue we are struggling with. I think we will try that "T" fitting solution..

I had a thought that maybe it was due to being fuel pump supplied vs gravity fed, but I did not know they made carbs with smaller metering valve inlets for service on fuel pump supplied systems.

Although it's no PWK, I think this 34mm PE should be a descent upgrade for him. So far as we can determine at this point, it is only running an aftermarket silencer. Haven't disassembled the engine yet so we don't know if any other mods are present. We'll be doing a complete tear-down for inspection over the coming weeks....

Oh, one other question...The 2 petcock setup, what purpose do they serve? Which does what? We did at one point try halfway closing the forward petcock and it seemed to alleviate the problem for the most part... Maybe just coinicidence???

[El Camexican]

Thank you very much El Camexican!

That is EXACTLY the issue we are struggling with. I think we will try that "T" fitting solution..

I had a thought that maybe it was due to being fuel pump supplied vs gravity fed, but I did not know they made carbs with smaller metering valve inlets for service on fuel pump supplied systems.

Although it's no PWK, I think this 34mm PE should be a descent upgrade for him. So far as we can determine at this point, it is only running an aftermarket silencer. Haven't disassembled the engine yet so we don't know if any other mods are present. We'll be doing a complete tear-down for inspection over the coming weeks....

Oh, one other question...The 2 petcock setup, what purpose do they serve? Which does what? We did at one point try halfway closing the forward petcock and it seemed to alleviate the problem for the most part... Maybe just coinicidence???

The guys on here say the second small petcock is not needed, well it does contain the only filter in the stock system, so I guess it did do something. Restricting the flow with it half closed is likely why the leaking stopped, but I wouldn’t want to drive like that. The other one seems to exist only to provide a reserve setting and plumbing. I've got to say if it wasn’t for the guys on here that explained this issue to me I’d likely have slit my wrists over this issue. Long live 3ww.com!

ADD: One last thing someone taught me that you might find handy is that when you first put on a dry carb and want to fire the trike, just blow in the air tank vent hose that runs up to the steering head and the pressure will fill the carb. Works great when you run out of fuel and switch over to reserve as well and saves a lot of kicking. Speaking of kicking, make sure the right side foot peg is in good condition and that it won’t allow the kick start lever to slip past it or you’ll be looking for an expensive clutch cover.

[RIDE-RED 250r]

MTS and El Camexican: Thanks so much for the help! :beer

We rigged it up with a "T" fitting as MTS pictured in that other thread and it works perfectly.

We just got done writing up the list of "needs" and "wants".... This is going to be fun. :)