Author Topic: CR750 Running (or not running!) issues  (Read 3200 times)

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #15 on: November 24, 2018, 10:48:54 PM »
Have you done a compression test on it.
No not yet but this problem has happened suddenly and all 4 plugs wet + thought it's unlikely that valve/bore problem on all 4 pots

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Offline Moorey

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Re: CR750 Running (or not running!) issues
« Reply #16 on: November 25, 2018, 01:32:20 PM »
Have you done a compression test on it.
No not yet but this problem has happened suddenly and all 4 plugs wet + thought it's unlikely that valve/bore problem on all 4 pots

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It is. Its just that you have stripped the carbs looking for bits of pods, I suppose its possible for it to have got to and stuck to the valves/seats .Unlikely but a possibility. Stranger things happen at times.

Offline MarkCR750

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Re: CR750 Running (or not running!) issues
« Reply #17 on: November 27, 2018, 09:34:46 PM »
Hi Phil, which carbs are you running, PD41’s with an accelerator pump?
Suzuki GT250A (Nostalgia)
1977 K7 CR750 (lookalike, what of I’m not sure)
Ducati 900SS (Soul & Speed)
Ducati M900 Monster (Handling & character)
Thruxton 1200 (suits me)
James Captain 197 (pure adrenaline, i.e. no brakes!)
"Eff yir gitten awvestear yir gooin te farst"
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Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #18 on: November 27, 2018, 09:41:16 PM »
Hi Phil, which carbs are you running, PD41’s with an accelerator pump?
Early 750 carbs (screw top type) Mark

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Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
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Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline MarkCR750

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Re: CR750 Running (or not running!) issues
« Reply #19 on: November 27, 2018, 10:12:14 PM »
Ok, mine started to get difficult to start, I found that giving the throttle a couple of sharp twists to make the accelerator pump squirt fuel into the intakes and then pressing the starter button regained instant starting, I think maybe my primary circuit is blocked, really must get around to taking carbs off and sorting, obviously you can’t try that because you don’t have an accelerator pump.
First I would try new plugs because it’s easy, but I think you’re issue could be fuelling , so I would..
1. Check the choke mechanism is working correctly
2. Check float heights and check that floats are not Punctured
3. Check the needle valves are seating/operating correctly
4. Check the carbs are receiving fuel from the tank and the tank isn’t forming a vacuum.
5. Give the carbs another clean.

Then, check the inlet rubbers for leaks.

Then alter your float heights away from the standard setting, if it gets better or worse you might be on to something.

Then because my bike ran badly with Pods until I grafted the original intake trumpets onto the front of them which makes me think pods are a bit crap I would get some velocity stacks, this doesn’t fit with your problem suddenly appearing but I think you’ll find the bike generally runs better with stacks, plus they look nice!

Also check your timing with a strobe gun so that you know the advance/retard is working

It will most likely be none of the above of course 🙂
Suzuki GT250A (Nostalgia)
1977 K7 CR750 (lookalike, what of I’m not sure)
Ducati 900SS (Soul & Speed)
Ducati M900 Monster (Handling & character)
Thruxton 1200 (suits me)
James Captain 197 (pure adrenaline, i.e. no brakes!)
"Eff yir gitten awvestear yir gooin te farst"
Sir J.Stewart.

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #20 on: November 27, 2018, 10:45:28 PM »
Ok, mine started to get difficult to start, I found that giving the throttle a couple of sharp twists to make the accelerator pump squirt fuel into the intakes and then pressing the starter button regained instant starting, I think maybe my primary circuit is blocked, really must get around to taking carbs off and sorting, obviously you can’t try that because you don’t have an accelerator pump.
First I would try new plugs because it’s easy, but I think you’re issue could be fuelling , so I would..
1. Check the choke mechanism is working correctly
2. Check float heights and check that floats are not Punctured
3. Check the needle valves are seating/operating correctly
4. Check the carbs are receiving fuel from the tank and the tank isn’t forming a vacuum.
5. Give the carbs another clean.

Then, check the inlet rubbers for leaks.

Then alter your float heights away from the standard setting, if it gets better or worse you might be on to something.

Then because my bike ran badly with Pods until I grafted the original intake trumpets onto the front of them which makes me think pods are a bit crap I would get some velocity stacks, this doesn’t fit with your problem suddenly appearing but I think you’ll find the bike generally runs better with stacks, plus they look nice!

Also check your timing with a strobe gun so that you know the advance/retard is working

It will most likely be none of the above of course 🙂

I've tried 1 - 5 Mark. The foam pods I've fitted have a smooth transition inside without the step on normal pods (read your post!). Probably will be going for stacks longer term and adjust settings accordingly. Have strobed and advancing ok as per Boyer instructions.

I'm leaning towards the way I've balanced the carbs - they are definitely balanced (on vac guages) but with all flooding on all 4 pots (after I balanced them) I'm wondering whether the needles are set 'too high' at start up  - if that makes sense. I have an original genuine Honda workshop manual that I'm sure says you balance them using the air screws (? - will re-check manual) - planning to bench balance them measuring slide cut outs distance (as I originally did when it started easily on first start up) then re-balance.
Just waiting for D7 plugs to arrive and try them.
I'm waiting for
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline MarkCR750

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Re: CR750 Running (or not running!) issues
« Reply #21 on: November 29, 2018, 05:25:30 PM »
Ok Phil, I’m never sure at times like this if it’s frustrating or interesting, both I suppose, first principle in trouble shooting is “what did I do just before it went wrong? “ so could be something that happened during the balance work if not the balancing itself (which is unlikely to the cause of the poor starting, but I know you know that :) )
Suzuki GT250A (Nostalgia)
1977 K7 CR750 (lookalike, what of I’m not sure)
Ducati 900SS (Soul & Speed)
Ducati M900 Monster (Handling & character)
Thruxton 1200 (suits me)
James Captain 197 (pure adrenaline, i.e. no brakes!)
"Eff yir gitten awvestear yir gooin te farst"
Sir J.Stewart.

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #22 on: November 29, 2018, 06:54:06 PM »
I agree - may be air screw adjustment relative to the balance of the carbs - may get time this weekend to have a look (barring Grand children arriving! I'm not too stressed about it - as long as I get it sorted by the spring!
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline CR750

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Re: CR750 Running (or not running!) issues
« Reply #23 on: November 29, 2018, 10:08:31 PM »
How much & how long have you had the fuel in the tank ? this could be your problem

Try draining the tank & fill it right up with a good premium fuel & then add some stabiliser for winter storage, if this sorts out the problem you then need to start it up every month or so until engine is warmed up. hope this helps
« Last Edit: November 29, 2018, 10:10:13 PM by CR750 »

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #24 on: November 29, 2018, 10:35:40 PM »
I've only been putting half a gallon in at a time as I have been waiting to get the CR replica fuel tap back from the guy who makes them (as it was leaking) and knew I would need to drain the tank. I have a cr250 motocross tap on at the moment (its not a tap issue as I've had that fitted since start up).
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #25 on: December 01, 2018, 07:35:56 PM »
Just got an hour in the garage away from grandkids. I think it's sorted (hopefully!). Tried messing with gradually weakening the mixture on the air screws - no change. Plugs still all wet.
Put the D7 plugs in and started 2nd kick - tinkered with slight adjustment of air screws and seems to be running fine. Will re-time and road test over the next week whenever the roads are dry.
Tried white spirit on NGK plugs that were in and the NGK lettering not coming off so whether they are fakes, just duff or the D7's are just better suited to the setup and change in weather, who knows!
Thanks for all your input guys
« Last Edit: December 01, 2018, 08:08:58 PM by philward »
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline Bryanj

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Re: CR750 Running (or not running!) issues
« Reply #26 on: December 01, 2018, 11:04:43 PM »
I always found that once wetted/fouled plugs may spark when laid on the head but fail under compression, only cure was the old Champion plug sandblaster.

Offline CR750

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Re: CR750 Running (or not running!) issues
« Reply #27 on: December 02, 2018, 12:02:33 PM »
I've only been putting half a gallon in at a time as I have been waiting to get the CR replica fuel tap back from the guy who makes them (as it was leaking) and knew I would need to drain the tank. I have a cr250 motocross tap on at the moment (its not a tap issue as I've had that fitted since start up).

The only problem with putting small amounts of petrol in the bike & leaving it stood for a while is that it will quickly attract moisture which will sit at the bottom of the tank & the watery fuel will be the 1st thing to fill the float bowls..
but I do understand, you will be emptying the tank to fit the new fuel tap so getting half a gallon out is much quicker than emptying a full tank..

PS.. I use Esso Synergy Supreme + 97 [ No ethanol in this, exceptions for certain areas of the UK ]
https://www.esso.co.uk/fuels-faqs
« Last Edit: December 02, 2018, 12:05:28 PM by CR750 »

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #28 on: December 02, 2018, 12:10:06 PM »
I use super unleaded in all my bikes to avoid the thernol related problems - until it gets put in that too!
Seemed to have sorted problem (see previous post) - duff plugs.
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline CR750

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Re: CR750 Running (or not running!) issues
« Reply #29 on: December 03, 2018, 12:04:10 PM »
I use super unleaded in all my bikes to avoid the thernol related problems - until it gets put in that too!
Seemed to have sorted problem (see previous post) - duff plugs.

Glad to hear you have sorted it !
The only super unleaded that has no ethanol added is Esso Synergy Supreme, all the other brands "Shell" "BP" etc all have ethanol added, usually 10% & this is going to increase...  >:(

 

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