Topic: stalls out when i give it throttle

[Tugboat]

Hi - new to the forum and finding it to be a great repository of helpful information. Just bought a '77 cb750k. It ran fine for a while, but was making a noise that I couldn't decide if it was normal or not. Cleaned the tank and put about a gallon of gas in. Rode it to work for a couple of days, trying to diagnose it. Ran low on gas, switched to Reserve, made it to the gas station, filled up, and now - starts and idles fine, but dies when i give it throttle. Barely made it home after it dying and only making it out of 1st using the clutch to keep rmp's high. Is this a top end (or compression) problem? or could it just be a carb issue? Don't want to spend the time re-doing the carbs now if I'm only going to have to do them again if I have to fix top end. Any advice appreciated!

[Queeg]

did you clean the carbs out.sounds like you might have got some crud in the float valve and possibly clogged it. does it have a filter?

[Ogri]

Does it stall if you engage the choke a little..or a lot ? Are all the exhaust pipes equally hot ? Looked at your air filter lately, or do you have aftermarket air filters ?

[Tugboat]

It doesn't stall if you engage the choke. And it does have pod filters on each carb. I should mention that before this problem popped up, the engine would have to warm up for about 5 minutes before it would run right. But that wouldn't be a carb thing, or would it? I did put a new inline filter in after cleaning the tank, so it shouldn't have sucked up anything. It's the sudden onset of the problem that has me worried. If it is a top-end thing, what would I be looking for?

[kslrr]

First do a complete tune up: Set ignition timing/gap, set valve clearances, set idle mixture, synch carbs.  Then diagnose issues.

[scunny]

remove the in line filter and see if it improves

[Ogri]

remove the in line filter and see if it improves

Yes good call, very likely it's become a little blocked (with sediment when you switched to reserve) and the bowls aren't getting enough fuel. There's enough for it to idle but when you open the throttle there's not enough in the reservoir to mix with the air from the pod filters. And because you have pod filters there's less vacuum so less fuel is being sucked in by the descending pistons. The gauze in your fuel tap might also be partially blocked, reducing the fuel flow even more.

[climbingaz]

As others have already mentioned, I'd bet money you sucked up some crud from the bottom of the tank when you ran it on reserve.  Before you go and completely tear down the engine and/or carbs, start with the small stuff.

This exact same problem you described happened to my Honda Magna a few years ago.  I refilled the tank completely, poured in some Seafoam and did my best to ride it till the tank was almost empty again.  After about a 100 miles, the problem completely went away.  But I'll admit - I did get lucky.

[wsup55]

I've been dealing with this EXACT same problem with my 77 750k after cleaning my tank up a few weeks ago.  Even with a new inline filter, some of the really small stuff found a way to get past the filter and dump crap into the carbs.  I just had them off to clean them for a second time and was surprised to find a rust colored jelly-like gunk in some of the bowls.  If your problem is like mine, you're going to have to do a thorough cleaning to all the carb jets and passageways and pay extra attention to checking out/cleaning your float valves and seats.  Also probably a good idea to check if your petcock is clear of debris and flowing correctly.

[Spanner 1]

Sounds like some or all of the accelerator pump nozzles in the carb throats are clogged....no squirt = dies just above idle. Easy to check, just twist throttle ( bowls full ) and observe carb throats for squirt of gas into carbs...bike doesn't need to be running either...... if thats the problem, carbs have to come off for full clean....lots of info/how to here....!

[Tugboat]

Thanks guys - Yep, took the fuel filter off last night and it was totally clogged with gunk. Hillariously so. Replaced the filter, cranked it up and was still having the same issue. So, took the carbs off and the bowls were totally full of the same gunk. One even had silicone gasket stuff floating in the bottom where someone had tried to repair one of the gaskets. Cleaned those up good last night, we'll see about the rest of it this weekend.