homemade rat racer

[MEASURE TWICE]

HH & CF what is it that the chain saw type or diaphragm type carb have to do with possibilities of burning exhaust valve or other negative results interaction?

What does the length of exhaust have to help and also the bend in the exhaust manifold do to help with problems arising from changing the carb to the diaphragm type?

I thought that when the chain saw carb is on the chain saw engine the muffler can't be that long as I would have noticed, so is it just that it is when put on a larger 4 stroke engine these things are important?

I did some searching on the web but did not maybe use the right word and didn't find information on this.

The one thing I did hear of before is the length of the carb manifold as it lengthens does increase the low end power of the engine for some reason.

Thanks

MT

 

[harlyhermansson]

they are not any connection between the carb type and the exoust valve overheating,i asked for those two things separably. i'm rebuilding the manifold and the exoust. i'v heard that the length of the exoust pipe can effect the engines performance and how hot it runns.
while the length of the intake tube has effect on tourq and top end,
a longer intake tube = a more stable air flow and more tourq.
shorter= more top end
sorry for the misunderstanding.

 

[curtisfox]

HH I think the best for you would be a 7hp Tecumseh carb like off a snowblower that has the low speed jet. http://www.alamia.us/Tecumseh_Carburetor_632615_p/rott-13147.htm. Looks like this. I am not sure if this is the right # or not but looks like this. I can get a # off mine if needed.
As far as the exaust is conserned there is enough restriction in a stock engine you don't have to worry about he heat, only thing is you should get it away from the engine with some kind of short pipe. The bigger the pipe the deapper the sound,I have seen guys take a 3" stack and put it on a garden tractor right next to the engine what a deap big engine sound. You say it ran good without the air cleaner it has some restriction then when you put it on. Dirty jet, bad air filter,check the plug for the right color? OXY-ACC torch tip cleaners work good for cleaning out the jets if that will help..............Curt

 

[harlyhermansson]

i'v ran a old tech carb before it was a dellorto 20mm, but i need to tilt the carb to get it out of the way of my leg while riding. so therefor i wanted to run a big chainsaw carb wich has been on a 80cc sthil from the 60s. ok so the pipe i have in mind should work great, yea but thar was a while ago, it was an old clogged up airclener, and i sorted that out a long time ago. but i did't really get along with the dellorto carb ether, very hard to tune. i'v tuned engines mostly chainsaws and weedwackers for 8years now so i got some basic knowledge about tuning but that carb never seem to work...

 

[MEASURE TWICE]

I was trying to understand what HH was needing to know to get the carb to work and fit and also not be in the way of leg while riding as I see you mention. The tilt of carb with float I understand you want to not have a problem with. This is where I showed my both right angle bend intake from other mower and also about 15 degree compensation to the tilt of my engine mount adapter part (was necessary to fit engine in frame).

Last what happened I was using a carb without any needle valve low or high adjust and was not going to try to mess with the jets. The engine I could get to run almost perfect when tinkering with the point gap timing, but high speed bogged down still. I found that after filter removed, I was on the wrong track and that the point gap can inter-react with the air gas mixture and maybe get near OK running, but that is not good enough I felt.

I got the filter for this carb that is recommended. It is also as I thought better to use a less restrictive filter and so I thought a pleated paper filter would be best, which is what I got. The housing part for it used on Ebay at less than $20 and got new pleated paper filter and the very thin foam prefilter and a new primer bulb locally at both Homedepot and Yardbirds Lawn Mower Shop.

Here I have pics of the low profile filter attached. It ran perfect and I didn’t even go back and adjust the breaker point gap any. It idles smooth and roars at full throttle. I will see about upload to Vimeo where I have videos.

Seems that I was able to find the new foam filter replacement for the filter housing I had been using and will eventually try to use it again to see if that filter could have worked with the carb since it already has connection I was going to route a corrugated hose to a point high on the frame for running in the desert. I would have to make that modification to this airfilter housing all over again and that something I probably will be doing as I’m pretty sure new or old foam filter are no match for the less restriction thin foam prefilter and pleated paper filter.

There are some things turned around like the left break lever and stuff, it is just when I store the bike it won’t fit otherwise and did not bother to turn it back around for the picture. The throttle cable still left un-hooked up in a bag too.

MT

 

[harlyhermansson]

im sorry iv'e been so slow on updates lately but it's been allot going on.
iv'e mounted the engine in the frame and i gave the engine some new life and a bit of a face lift, pix coming when i get home from school.

 

[harlyhermansson]

sorry i haven't uploaded any pics yet, but there has been really ****ty weather and the camera have been a bit weird.. hopefully i can get pics in the weekend and i might show you guys a other little project of mine as well...