VH4D update

Hi all,
Here"s the situation, for those who have been following this. I had some spitting and light backfiring thru the carb so I decided to go back and do over a few things so here is where I am Brand new Zenith carb, Brand new fuel pump, brand new spark plugs, all new fuel lines and related fittings. IT STILL SPITS AND BACKFIRES ???? I"m at a loss this time and running out of time to get this done. I do want to mention that when I close the choke a little the spitting and popping goes away. I"m thinking maybe my timing is off a little, I may try to adjust the timing again , what do you all think ??? Timing???

All do you guys agree with this statement I just found? " if the timing is advanced too much then when the piston comes up to fire your intake valve is still cracked open a little, therefor pushing burning fuel back thru the intake causing the spitting and popping ?" End quote !

Ok just did some research, checked my NEW plugs and they are very black and very dry , according to my research that also points in some cases to timing, can"t be a carb issue it"s brand new and when I turn the air fuel mixture screw in or out nothing changes . Pretty sure it"s the timing.

This does not sound like a timing issue. Sounds like still too lean.

The black plugs could be caused by either running with the choke partially closed, starting and stopping and never getting under power or up to temp, or mixture so lean it's not completely burning the charge.

The mixture screw, you say it does nothing? Are you adjusting the screw at idle? All that adjusts is idle mixture and will have minimal effect on the main mixture.

Now that you have 3 carbs to work with, open them up and look at the numbers on the main jet in all 3. See if there is a larger jet in any of them. If there is, put it in your new carb and try it. If all are the same, invest in some jet drills and drill ONE or TWO of them out, keep the original jet so you can put it back if necessary. Keep notes on what you've done, drill only to the next closest size, do one thing at a time so you know what works and what doesn't.

Back to the timing issue...

Retarded timing will cause backfiring out the carb. Not sure why, but it does.

Advanced timing will show as kicking back while starting, spark knock (hard to hear on an air cooled).

If you can find timing marks, you can static time it with a test light or ohm meter. Turn the engine in the direction it normally runs. Stop 2 to 4 degrees before TDC. Set the points to open at that point. This will put you close enough to start and run.

Run the engine with the choke on. Run it under load and see if it smokes, that it may be too rich. If it doesn't smoke run the snot out of it under load. I have to do that on my snowblower and its 17 years old. I've been using it a lot this past week. Hal

I've got a 610 bobcat with the VH4D. I'm thinking along with others on this board that you're running a little lean, mine will spit when it's cold need to keep the choke out until it warms up then it smooths out and runs fine. Another thing is that you'll need to check the float height when you get to using it. My float is adjusted down so that you don't get as much gas in the bowl. So when you get the loader nose down in a hole it doesn't flood itself out.