More CB750 fun

The Older Gentleman wrote:
>
> Yes. Ultrasonic cleaning - the only way to be sure.
>
Ok but if the jets are clear, what is left to clean?

Cheers,

Nick

--

CCM R30, CB750 (broken)
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Nick Wilson wrote:

> So, gentlemen, the story so far is that my CB750 carbs were blocked.
> I took them off and cleaned out the jets - three jets per carb.
>
> Still doesn't work. It runs fine on easystart - if I keep spraying it
> runs continuously.
>
> Did I miss something in the carbs? What else could it be? I guess
> easystart is a lot easier to ignite and maybe a very weak spark will
> let it run on easystart but not petrol?

Did you check the spark? Do you have ample compression?

> Is this likely or should I be looking at the carbs again?

If they were completely gunged up, yes.

--
Morini Corsaro 125 | CB450 K4 | XL250 Motosport | 900SSD | K1100LT
Laverda SF2|Harley FXD BOTAFOF #33
The UKRMC FAQ: http://www.unixconsult.co.uk/bike/ukrmcfaq.html
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Timo Geusch wrote:

> > Did I miss something in the carbs? What else could it be? I guess
> > easystart is a lot easier to ignite and maybe a very weak spark will
> > let it run on easystart but not petrol?
>
> Did you check the spark? Do you have ample compression?

If it runs on easystart it's a pretty safe bet it's fuel related.

--
Simon
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Nick Wilson writes:

> The Older Gentleman wrote:
>>
>> Yes. Ultrasonic cleaning - the only way to be sure.
>>
> Ok but if the jets are clear, what is left to clean?

First, you can't tell if the jets are really clean - they're open now
but that doesn't mean that they haven't got some crud left in them that
reduces the size of the jet.

Also, I assume that you at least made an attempt at cleaning out the air
passages in the carb body?

Also, have you checked that the float needle valves are not sticking,
that the float height is correct and all the other fun problems you can
get with carbs?

--
Morini Corsaro 125 | CB450 K4 | XL250 Motosport | 900SSD | K1100LT
Laverda SF2 | Harley FXD BOTAFOF #33
The UKRMC FAQ: http://www.unixconsult.co.uk/bike/ukrmcfaq.html
 >> Stay informed about: More CB750 fun 

Nick Wilson wrote:

> > Yes. Ultrasonic cleaning - the only way to be sure.
> >
> Ok but if the jets are clear, what is left to clean?

All the little passages and galleries in the carbs. Ultrasonic cleaning
is the next step.

At least you're getting good at removing and refitting the bloody things.

--
Simon
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Timo Geusch wrote:
>
> Did you check the spark? Do you have ample compression?
>
I only checked the spark with one of those neon things. No I've not
checked the compression but the bike ran well before it was garaged. As
I said it runs OK on easystart so there can't be *that* much wrong with
it.


>> Is this likely or should I be looking at the carbs again?
>
> If they were completely gunged up, yes.
>

Hmm... I' don't know. They didn't look particularly dirty inside but all
the jets were blocked. I removed and soaked the jets in carb cleaner,
then blew them out with the carb cleaner aerosol.

Cheers,

Nick

--

CCM R30, CB750 (broken)
 >> Stay informed about: More CB750 fun 

Nick Wilson writes:

> Timo Geusch wrote:
>>
>> Did you check the spark? Do you have ample compression?
>>
> I only checked the spark with one of those neon things. No I've not
> checked the compression but the bike ran well before it was
> garaged. As I said it runs OK on easystart so there can't be *that*
> much wrong with it.

That very much depends on how long you're running it on Easystart...

>>> Is this likely or should I be looking at the carbs again?
>>
>> If they were completely gunged up, yes.
>>
>
> Hmm... I' don't know. They didn't look particularly dirty inside but
> all the jets were blocked. I removed and soaked the jets in carb
> cleaner, then blew them out with the carb cleaner aerosol.

Yes, but did you only blow through the jets or also the various other
orifices in the carb body itself?

--
Morini Corsaro 125 | CB450 K4 | XL250 Motosport | 900SSD | K1100LT
Laverda SF2 | Harley FXD BOTAFOF #33
The UKRMC FAQ: http://www.unixconsult.co.uk/bike/ukrmcfaq.html
 >> Stay informed about: More CB750 fun 

Timo Geusch wrote:
> Nick Wilson writes:
> First, you can't tell if the jets are really clean - they're open now
> but that doesn't mean that they haven't got some crud left in them that
> reduces the size of the jet.
>
Hmm. I guess so. There was a little sediment in the float bwls but they
are thoroughly clean now.


> Also, I assume that you at least made an attempt at cleaning out the air
> passages in the carb body?

The only air passage I cleaned out is the idle air adjuster (I think).
There are passages to make the piston rise but they are quite big and
were clear. Are there other air passages?

>
> Also, have you checked that the float needle valves are not sticking,
> that the float height is correct and all the other fun problems you can
> get with carbs?
>

The float valves are OK. Oddly, I can see no means of adjusting the
height. The floats are all plastic and pivot on a steel pin. The Haynes
manual shows you bending a tang on the float but it differs from my
carburators.

Cheers,

Nick

--

CCM R30, CB750 (broken)
 >> Stay informed about: More CB750 fun 

Nick Wilson writes:

> Timo Geusch wrote:
>> Nick Wilson writes:
>> First, you can't tell if the jets are really clean - they're open now
>> but that doesn't mean that they haven't got some crud left in them that
>> reduces the size of the jet.
>>
> Hmm. I guess so. There was a little sediment in the float bwls but
> they are thoroughly clean now.
>
>
>> Also, I assume that you at least made an attempt at cleaning out the air
>> passages in the carb body?
>
> The only air passage I cleaned out is the idle air adjuster (I
> think). There are passages to make the piston rise but they are quite
> big and were clear. Are there other air passages?

Did you blow through all the passages that the jets screw into?

>> Also, have you checked that the float needle valves are not sticking,
>> that the float height is correct and all the other fun problems you can
>> get with carbs?
>>
>
> The float valves are OK. Oddly, I can see no means of adjusting the
> height. The floats are all plastic and pivot on a steel pin. The
> Haynes manual shows you bending a tang on the float but it differs
> from my carburators.

There should be a way of adjusting them - the float bodies themselves
are always plastic in all Japanese bikes I've played with, but usually
the bit the pivot goes through is metal.

Of course the fact that Haynes shows something different isn't exactly
news...

--
Morini Corsaro 125 | CB450 K4 | XL250 Motosport | 900SSD | K1100LT
Laverda SF2 | Harley FXD BOTAFOF #33
The UKRMC FAQ: http://www.unixconsult.co.uk/bike/ukrmcfaq.html
 >> Stay informed about: More CB750 fun 

Timo Geusch wrote:
>>
>
> Did you blow through all the passages that the jets screw into?
>
Yes, though they are quite big.

I've got the carbs back off - I'll have another go at cleaning them and
if that doesn't work I'll give up and book it in with my local man.

>
> There should be a way of adjusting them - the float bodies themselves
> are always plastic in all Japanese bikes I've played with, but usually
> the bit the pivot goes through is metal.

These are completely plastic. I'll take a photo.

>
> Of course the fact that Haynes shows something different isn't exactly
> news...
>

To be fair, mine is a later model. There is a supplement for the later
ones but no carb photos.

Cheers,

Nick

--

CCM R30, CB750 (broken)
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sweller wrote:
> Timo Geusch wrote:
>
>> Did you check the spark? Do you have ample compression?
>
> If it runs on easystart it's a pretty safe bet it's fuel related.
>

That's what I'm thinking (and hoping).

Cheers,

Nick
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sweller wrote:
> All the little passages and galleries in the carbs. Ultrasonic cleaning
> is the next step.
>
> At least you're getting good at removing and refitting the bloody things.
>
True. I find it quite easy now...

Cheers,

Nick
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"Nick Wilson" wrote in message

> sweller wrote:
> > Timo Geusch wrote:
> >
> >> Did you check the spark? Do you have ample compression?
> >
> > If it runs on easystart it's a pretty safe bet it's fuel related.
> >
>
> That's what I'm thinking (and hoping).
>
> Cheers,
>
> Nick

Does it run at all without the Easystart?

You did remove the pipe(s) to make sure petrol is actually getting to the
carbs?

Oily
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