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K7 carb help.

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zippy!:
Hi all, firstly sorry to drop in and be a pain! I hope the moderators allow my post.

I have had help before with missing bits and thanks to you guys being a great community I was helped out massively.

I am running some CB750 K7 carbs on a Hillman Imp. Yes you read that right! I bought them off an imp trader and thought I would give them a go, and prevailed, despite many a time I could have given up.

The car has only done a few hundred miles since restoration and bar needing a proper tune, it was running fairly well, albeit a bit rich. Pain to start due to the chokes being removed but once on the go not too bad. At first the custom manifold we made didn't allow room for air filters, so mesh it was for a while. I dropped the clips to make up for this.

Over winter while off the road, the manifold was modified to accommodate room for filters. Started up and ran about as well as before.

One thing I did have an issue with is the odd bork when cornering harder to the left. The carbs are mounted on the car in line from rear to front with air intake to offside (cyl 1 is at the back of the car). This happened the other day to the point where she cut out. I think I may have flooded trying to re-start, and being towed an hour or so later, tried to bump it and got only a couple of big misfires. (Could this have further hindered things).

Since then, I've checked I have spark, got fuel to the carbs and got compression. With the carbs off I can see the accelerator pump is working ok. Not sure how I can check the main jets. However when turning over, I don't think fuel is reaching the cylinders. The plugs aren't getting wet, even when really turning over for a while.

I did briefly get it to make a little "hissy cough" when turning over a few times when giving a brief pump of the throttle prior to turning over.

I'm not any sort of carb expert, but I was wondering if there is anything on the carbs I should be paying particular attention to. Plus does anyone ever have an issue with borking out? Though my case was left hand bends, on a bike it would be the equivalent of a hard stop!

In any case I hope this makes sense. Thanks in advance for any kind input / info that can be provided.

hairygit:
Interesting conversion! Many years ago I owned a Bond Bug, and we fitted CB900F carbs to it, went like the clappers, and even gave 70+ to the gallon! Truthful answer is I always advise anyone with K7 or F2 carbs messing about to dump them and fit carbs from another CB750 model. The PD carbs are well known for clogging up internally due to the tiny internal passageways, they are okay (acceptable) when spotlessly clean and well set up, but the tiniest bit of crud in them is a nightmare. I would certainly get them stripped and thoroughly cleaned again, and consider putting a diesel filter head in the fuel line (The sort that are generally bolted to the bulkhead of diesel Landrovers) should cost peanuts at a scrapyard, and the filter elements are relatively cheap and long lasting. Most likely cause of crud getting in the carbs, particularly when cornering hard is the fuel in the tank sloshing about and washing particles of rust from the inside of the tank into the fuel line. Did you clean or seal the tank before doing the conversion? Or has it got 40-50yrs of rust and scale floating around in it? :o Also, bike carbs are made for gravity feed (Except for a few oddities like Goldwings) and the fuel pump pressure may be overpowering the float valves, particularly if it is a mechanical pump rather than electric. Remember to flush the fuel lines through as well, otherwise the whole lot will need stripping and cleaning again. :-[

zippy!:
I bet the bond was fun!

Thanks for the reply.

I've got an alloy foam filled fuel tank so that should be well baffled. I try to keep it full too. All new fuel lines (though rubber), running with a facet electric fuel pump with small inline filter, then in to a larger filter king fuel pressure regulator and filter. Pressure should be ok as when it was too much, I got fuel from the drains.

Will take them off and check all of the passages are clear. Do you know if any other 750 carbs will fit straight in to the inlet manifold (size and spacing)? The carbs are held on by silicone hoses so a few mm either way will be ok!

Cheers

hairygit:
In that case, any bank of CB750 carbs can be made to fit, as only the intake rubbers need changing on a K7 or F2

Sent from my X6pro using Tapatalk

zippy!:
That's great news. Sorry to ask further, but is any particular year better than another? I.e. For setting up or reliability etc.

Trust me to have picked up the worst ones. I knew I was in for trouble when I found out they only used them for one year!

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