Topic: 750 Struggles to Take Off From Cold Start

[jakec]

Has anyone had an experience with a 750 where the bike will start right up and idle, but if you put a load on it it wants to die? From a cold start first kick, I can sit there and idle for any amount of time. It is a bit hesitant to crack the throttle. And the bike will want to die when you put a load on.

It kind of feels like a fuel delivery problem when I crack the throttle. I have everything 100% stock, with dual feed petcock. It's a k0 with original carbs. The bike runs amazing and idles nicely at the 1000 mark per the manual. I'm not running any fuel filters due to experience with dual feed and filters creating a vapor lock. The way the fuel lines are routed the filters would be horizontal making the problem even worse than on a 350. Floats and valves are all new and adjusted. The tank has been de rusted but could have debris floating around, which may be clogging the petcock.

I had this issue before with my 750 chopper but I assumed that was due to the poor tuning at the time. Since improving the tune this problem seems to have gone away. That bike also has later round top carbs, but I'm using a single feed petcock and a splitter.

What I do now when riding the bike is just goose the throttle after warming up, and feather the clutch very very lightly until the bike awkwardly takes off. Once I start moving everything is fine and I can ride all day, and the problem wont come back until another cold start (at least 1-2 days sitting). So I'm wondering if it is fuel delivery, how does it get better once you start going?

[seanbarney41]

I have had lots of 750's that do exactly that, some that don't, and many that do that plus will not idle without help from the throttle until the engine has warmed.

[newday777]

Have you cleaned the emulsion tubes under the low speed jets? If so how did you clean them? It sounds like a slightly plugged low speed circuit.
Have you opened the bowl of the petcock and removed the brass screen to inspect for debris in the screen?

[newday777]

The other thing to check is vacuum leaks at the intake to the head.
When the motor is cold, the rubber intakes can be loose on the cold aluminum intakes, the aluminum intakes expand as the motor heats up and will seal any leak there might be when cold as you are experiencing.

Hondaman posted this last week.

[Scootch]

Maybe check fuel cap, petcock, fuel lines, fuel line routing, etc. Air lock ? Try popping the fuel cap to make sure the cap vent is working...

[jakec]

Well there was definitely some crud in the bowl of the petcock. But it looked like the screen was doing its job. I've had a 550 with a rusty tank where I did the same check and the bowl was almost full, bike was running fine tho.

I'm able to ride this bike 120 miles on a tank without opening the lid, so I don't think venting or anything related to routing is the problem. After reading the replies here I think it must be the intake boots. I did an air leak test when I was doing my carb sync, but that was with the bike already warmed up. My question now is, will new intake boots (genuine) fix the problem? I know they are pretty expensive.

[newday777]

Yes if you have air leak when cold, only new genuine Honda intake boots will cure it, and new Honda bands will cure it. Yes they are expensive. At least we can still get them new.
Aftermarket have high failure rates.

[seanbarney41]

i think you should just stick to the models with electronic fuel injection

[BenelliSEI]

Lot’s of excellent advice above. Here’s another thing to check:

Are you using the original 4 X pull cable throttle carbs? Do you have the rubber gaskets under the screw on tops?

That cold start hesitation is very much a symptom of those missing. You will have a very hard time getting a consistent carb sync without them. I use the later style and just knock a larger centre hole with a 1/2” gasket punch.

[jakec]

Yea I’m using the 4x4 cable, and I did install the rubber gaskets at the top of the carbs. The intake boots seems more and more plausible when I think about it because I went through a lot of iterations in the spring & summer getting everything right. And the hesitation issue only popped up when it started getting colder. Everything was great back in august but now that the temps have dropped to the low 40s I could see how the issue would present itself.

[scottly]

i think you should just stick to the models with electronic fuel injection

Jake, you need to learn how to properly use the manual choke for cold starting and warm-up, before chasing phantom vacuum leaks that mysteriously disappear once the motor has had a chance to warm up to operating temperature.    

[BenelliSEI]

i think you should just stick to the models with electronic fuel injection

Jake, you need to learn how to properly use the manual choke for cold starting and warm-up, before chasing phantom vacuum leaks that mysteriously disappear once the motor has had a chance to warm up to operating temperature.    

I’m inclined to agree.