Diaphragm vs Float

[AmTeC]

Alright folks, I need the pros and cons of the tecumseh float vs dippy carb to make a decision on what to put on my sketchy tecumseh HS40 powered mountain bike

And I'm talking the tecumseh specific pros and cons of the carbs, I know that diaphragm carbys operate in any position.

I mean, what are performance and reliability pros and cons, do they perform equally? is one better than the other? Can a dippy carb support as low of an idle as the floaties? response time? reliability? Venturi size?

You see, I hate the float carbs, I have terrible luck with them. It seems every 3 months I need to retune it. The floats occasionally sticks opens and pisses all the fuel onto the floor, and this is with like 3 different carbs, not just one. Every bump I hit seems to make the engine run funny, probably the float bouncing around. But I understand many minibikes used the standard float carbs, so they must not be that bad I guess, maybe I'm doing something wrong. I thought about swapping it with a tecumseh diaphragm carby since I've had great experiences with walbro pumper carbs in the past. But I dont want to lose power, I like a nice responsive hesitation free engine, and there just isn't that much info available about these things, Like Im not even sure if they have fuel pumps built in like the walbros do.

 

[jp1961]

Hello,

Is the HS40 a two or four stoke engine?

I would say a float carb wouldn't work well in a bumpy environment of a mountain bike,but you've already discovered that.

I also can't say if a engine designed for a float carb would even work with a diaphragm type carb.

Tecumseh made the TC200 and TC300 2 stroke engine that did use a diaphragm carb, not sure if it had an internal pump or not (although the main principle of a diaphragm is to use crankcase pulses to push the fuel into the carb). This might be the type engine you'd want for a mountain bike conversion.

The TC200 and TC300 can be found on Mantis (Sears too) type tillers, one company actually used them on a weed whackers and I have a string trimmer that had wheels on it, so it shouldn't be hard to come by.

Regards

Jeff

 

[AmTeC]

Hello,

Is the HS40 a two or four stoke engine?


I also can't say if a engine designed for a float carb would even work with a diaphragm type carb.

Tecumseh made the TC200 and TC300 2 stroke engine that did use a diaphragm carb, not sure if it had an internal pump or not (although the main principle of a diaphragm is to use crankcase pulses to push the fuel into the carb). This might be the type engine you'd want for a mountain bike conversion.


Jeff

The HS40 is a 4 stroke

Tecumseh made a carb that worked on their 4 stroke engines 4 hp and lower, it was the same one they used on some of their 2 stroke engines. It doesnt use crankcase impulses to work, instead it uses the pulses from the intake to operate, similar to a briggs pulsajet I guess. Im just wondering whether there would be some performance losses switching over to one of those, as I dont see them anywhere near as often as tecumseh's bowl design. most of the tecumseh 4 stroke minibikes seem to use bowl carbs, which is odd considering mine never liked bumps or hills much. Although there were certainly some diaphragm carby minibikes out there too.

Today I tried cleaning my bowl carb and found lots of rust inside, and it seems to work fine, revs up, idles nicely, responds quick, but stalls or hesitates on return to idle from any open throttle position. The Low needle jet looks like someone took a chunk out with a grinder, and all my spare needles are too short. Might as well replace the whole thing at this point, but the question remains

Bowl or dippy?

 

[bertsmobile1]

Dump the tecumseh and fit a Tillotsen diaphragm carb.
They are a lot lot lot better and used on a lot of racing mowers and carts because for some idiot reason people will pay a lot more for their toys than they will for their tools.
Chase up the cart shops or contact Tillotsen direct.

 

[AmTeC]

Dump the tecumseh and fit a Tillotsen diaphragm carb.
They are a lot lot lot better and used on a lot of racing mowers and carts because for some idiot reason people will pay a lot more for their toys than they will for their tools.
Chase up the cart shops or contact Tillotsen direct.

I thought about it, I did some research, and supposedly, tecumseh and briggs engines fitted with tillotson carbs don't idle well, as the carbs were never designed to support such a low rpm. Could be total bs, but I thought I'd go with what the engine was made for, even if it is crap. Also isn't there some impulse line I need to hook up to get a tilly carb working?

 

[tom3]

Every dirt bike and four wheeler we've had did have the float bowl type carb. Seems to work fine every way but upside down.

 

[Bob E]

I prefer float bowls for maintenance. I can usually pull those apart and clean them many times before worrying about replacing seals. Seems like whenever I pull a diaphragm carb apart I should have a new diaphragm ready and waiting...
I have an old LAV35 on a shredder/mulcher that has one of the carbs your talking about. Having the high and low adjustments is pretty nice, and would likely work better with varying engine speeds.

 

[tadawson]

You described your problem - stumble returning to idle.

You clearly described what is likely the cause - a mangled idle needle.

What I don't understand is why you want to throw parts at it instead of fixing the problem! Short of inverted or really odd angles (as on a weedwhacker) there should be nothing that a sanely driven mini bike can do that a float carb won't work for. The large diameter (ring) of most floats sees the average level in the bowl and compensates. Heck, I have likelt tiltes/bumped my mowers more that what a mini bike engine should see, and never a blip! Get a kit for your carb, freshen it up and tune it properly, and *then* evaluate the situation!

 

[AmTeC]

You described your problem - stumble returning to idle.

You clearly described what is likely the cause - a mangled idle needle.

What I don't understand is why you want to throw parts at it instead of fixing the problem! Short of inverted or really odd angles (as on a weedwhacker) there should be nothing that a sanely driven mini bike can do that a float carb won't work for. The large diameter (ring) of most floats sees the average level in the bowl and compensates. Heck, I have likelt tiltes/bumped my mowers more that what a mini bike engine should see, and never a blip! Get a kit for your carb, freshen it up and tune it properly, and *then* evaluate the situation!

I'm fine with throwing parts at something if that means I might get a better result. Tec float carbs have always been super inconsistent for me, whether it be floats sticking open for no observable reason, requiring the high needle to be retuned if the humidity changes outside, hard cold starts, hard hot starts. if I drain them for storage they seem to rust internally for some reason, if I leave the gas in them for a couple months they wont start easily (not a problem for my briggs engines, gas does not go bad quickly where I live). I know float carbs can handle bumps and whatnot, but the three I tested dont do a very good job, the floats are adjusted to spec. Who really knows, I know some tec carbs had float springs for bumpy applications, This is not one of those carbs, and Im not sure if minibike tecs had this spring.

And Im fairly certain swapping a carb is less work that taking off the old one and totally rebuilding it... it is just plug and play after all, its not like I need to fabricate a whole new manifold and governor linkage, tec dippy carbs bolt right up.