1995 Speedster engine RPM surge

[yamahauler99]

Recently rebuilt all 4 carbs on a 1995 speedster with 657 engines. One engine runs great boat shoots out of the hole but then about 4-6 seconds of seemingly perfect running port side engine will drop down to about 4K rpms for about 2-3 seconds then it will pop right back to full RPMs

all new fuel lines new petcocks new water separators

I have a ton of history in this boat, my father in law bought it new then handed it down.
Let me know if you have any questions

 

[yamahauler99]

anyone on today? Maybe electrical???

 

[rusty nail]

sounds like a symptom of fuel starvation. Those 4-6 seconds are a result of fuel being ready to go, you use it up, then the fuel cannot keep up. so it is being choked at any number of those locations you changed. wrong size lines, fuel filter partially plugged or wrong fuel filter, fuel selector bad, etc.

 

[yamahauler99]

Thanks!!! I used the same of size fuel line when rebuilding the fuel sys. Was reading this morning that I could switch the fuel supply lines

to see if the issue followes the fuel supply or stays with the engine.
Also my in original post I didn’t even know pop off pressure was a thing. Now I have the pop off pressure set on all 4 carbs.
Will try to run it again today.

Also just because I could, I put the poor running carbs on the good running engine to see what happens there.

Another thing that I didn’t mention that may matter

I’m using just a single battery right now. Had a new atv battery and didn’t want to spend the money on two new ones till I verified that engines ran well. I literate just have both positives and both negatives wired to the one battery.

 

[rusty nail]

sounds like you are trying to narrow it down. Good luck

 

[yamahauler99]

Just wanted to give an update.
Took the boat out yesterday with a temp fuel tank connected directly to the carbs and she ran like a champ. So now we can start eliminating what’s NOT wrong in the newly rebuilt fuel system