Hey gang -

Last year my uncle & I bought a '90 750 Sport as a fixer-upper and it's finally running again.

Sparing you all the gorey details, here's my dilemma. The bike has had the stock Weber and airbox tossed in exchange for a set of 38mm carbs from a later model 900ss. It has long intake runners, and the carbs are connected. The carb mouths are just a few mm from the battery. It has Cobra F1 slip-ons. Anyhow, I had the bike worked on recently - new belts, valves checked, new plugs, carbs torn down and cleaned throroughly, jetting adjusted, and installed foam pod filters on the carbs.

My mechanic's first comment is these carbs are way too big. He said they'll be perfect if we do a high compression piston kit down the road, but right now they are overkill and were extremely hard to tune (4 hours on the dyno getting it right). He still isn't happy with the performance. But the bike runs really good compared to before. He measuerd 61 hp and 46 lb-ft torque at the rear wheel.

The shop is about an hour's ride from my home, and I rode it home with no problems - ran flawlessly. But the more I ride it, the more I feel a hesitation from time to time. Kind of feels like a fuel starvation situation - not a misfire or lack of spark situation. It happens at steady throttle, usually above 45 or so MPH, and usually when it's in traffic. Not sure if it's temperature related or not yet (it's been pretty hot here, around 85 to 90 degrees F). Definitely more noticable in traffic than running alone on the road.

My question is... is this normal for an open-pod setup? Every other bike I've ever owned has had an airbox/pipe/jetkit so I don't have anything to compare it to.

Here's a pic. Still needs to get the Harley grips taken off, install the new tires, install new brakes pads, get some stainless steel braided front lines, and install bar-end mirrors. Then we're going to ride the wheels off it. :thumbup:

:confused:
If it happens from time to time, this looks more likely to be a fuel supply trouble.
The fuel filter is brand new?
how does the pipeline run?
the carbs look to be placed in quite an high position, this might need a fuel pump (like the weber has)
Anyway, the 38 mikuni properly jetted fit very well on 750 engines :thumbup:

I have heard, that Mikunis NEED GOOD AIRBOX to function well, so i am wondering now, that U have fitted foam air filters to Your bike... :confused:

Good questions, thanks for you responses.

No we didn't replace the fuel filter, but as luck would have it there's a whole post on just that subject on this very forum. I'll do that first.

As for the airbox question, you are correct we only have pod filters, which is something I was concerned about. There's nothing to keep engine heat out of the motor. Finnpaso is that something you heard related to the Mikunis as well?

Hang on, I just remembered something... when I replaced the fuel lines I did add an in-line fuel filter to the line between the tank and the carbs. It's one of the clear filters that you can watch fuel flow through.

Is there one inside the tank as well? There is a fuel pump in there, I can hear it whirring when I turn the key to the On position.

There's a pre-filter which is kind of like a big long tea bag. The fuel pump and a filter if it's like a typical SS setup.

It does sound a lot like fuel starvation. But... the fuel pump and plumbing must be made right first to eliminate it from the equation.

Awesome! Thanks Jon, I'll take it apart and see what I find...