Inyourface1650

Hey guys, got my Nighthawk back up and running with a new engine works great - mostly. I am running the new engine, but my old carbs on it.

I have been having problems with fuel delivery however. It will cruise along fine. Often after a WOT run, even with a couple gallons of gas in the tank, it will essentially run out of fuel and either stumble along at 30 mph misfiring or just cut out completely. Looking at my clear (plastic) fuel filter its obvious there is no fuel in the lines. Today I took off the tank, and petcock and blew air through it (all ways) and the petcock is good. Similarily I took off the line from the tank to the carbs (with the filter) and made sure those were good. I even attached a hose to the tank and ran it to a gas can, and all the settings on the petcock work fine, including off. However when I hook the tank back up, the fuel filter is NOT filling with fuel.

How does fuel go to the carbs(I'm new to carbs sorry). Is it vaccumm or just gravity feed into the bowls?

help!

ragnaroek

is the tank venting properly?

MSchu

check your breather circuit in the tank, your probably getting fuel starvation due to a vacuum issue

Inyourface1650

Well....as far as breathers go....as far as I know I don't have one. Unless its integral with the gas cap, which it might be because that sucker is NOT water/gas tight lol. I figured it was, flipped the tank, and had a mess . Other then that all I have the is the fuel level sender/float which of course doesn't work.....

I do have a leak in the back of the tank, but its small...

EDIT: also the haynes manual is miserable when it comes to fuel delivery diagnoses. I guess its too simple...

MSchu

there should be a small hole in the tank around the cap area... make sure that venting is clear

ragnaroek

if he turned the tank up-side-down and fuel poured out, i would guess that it's venting. are the carb breathers working properly? float heights correct/not sticking?

the dohc carbs are ridiculously complicated compared to the sohc carbs. have you asked on the cb1100f forum? i know that it's specifically for the 1100f, but there are people on there who also know about the dohc 750s. http://www.cb1100f.net/

MSchu

If those floats are sinking that bike wont run correctly

Inyourface1650

I appreciate all the insight guys. The fuel was pouring out all around the cap, not just from a breather (too much fuel). I did find the little hole in the gas cap(not on the tank, wierd eh?), and ethered the heck out of the thing, and that seems to have solved the problem for now. It hasn't died on me in a good solid week. Knock on wood. lol. its been a journey.

Now If I could just figure out why it runs so terribly at 7500RPM+...but that's another thread.

HansJr

are all the vacuum lines hooked up correctly on the carb?? ive had problems with my older kawi's with a vacuum hose being routed wrong when i took them off and replaced them. also check and make sure the float height is correct.

Inyourface1650

Carbs only have one vaccumm line and it looks like it goes to a fuel regulator or something.....

it died on me on saterday, I finally actually found the problem. The previous owner had put in a in line fuel filter. I assumed this was correct, and replaced that fuel filter with a new one from autozone when I put the new engine in. Well, when the bike is low on fuel, it was having problems gravity feeding through that filter (which is designed to have a fuel pump behind it). as soon as I removed that filter, fuel is flowing great now!

I guess there is supposed to be a honda factory filter on the petcock tube, which there is not...I will have to pick one up and install it.

I almost wonder if its getting to much fuel now however, the carbs have lots of dead spots now. They were just rebuilt before I bought the bike, I bet incorrectly. Might explain why the thing won't idle when its cold either, even choked. If its not something its another grrrrr

MSchu

hmm...

most carbed bikes don't use filters because you are not employing an injector... the part that always get clogged on modern induction systems when the fuel is not clean.