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

Offline philward

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CR750 Running (or not running!) issues
« on: November 23, 2018, 10:53:07 PM »
I’m still trying to set up the CR750 to run correctly and was making reasonable progress. However, now the bike struggles to start, occasionally fires and runs (10 seconds) really rough before cutting out and won’t start again.

Reminder of initial set up – 836 Cruzinimage standard compression kit, standard carbs/jetting, foam pod filters, Boyer Micro Ignition/power coils, Moonpie race exhaust with K0 baffles (also, race alternator which has light weight rotor and works with starter motor clutch removed). Carbs bench set up (carb piston cut out height)

Here’s what I have done so far:-

On above set up and first start, started 6th kick and run as per video below. Fuel starvation in mid-range when riding.

https://www.youtube.com/watch?v=YmL8YYWeUMo

Put 135 mains in and raised needle to 2nd from bottom clip (2nd richest) – cured fuel starvation issue in mid range (not revved in higher range yet) – occasional back fire through carbs on start up and plugs black when run for a time at low revs (on a run were I was able to keep revs in mid range, they aren’t a bad colour) .

Rev counter sorted by Smiths so timed with strobe – no difference

Checked tappits and Balanced carbs on vac gauges using carb top adjusters (not air screw adjustment as in a Honda workshop manual I have?) – little change (obviously engine well warmed up at this time) – no change to above. At this point bike was running acceptably well except for the occasional back fire through carbs on start up and plugs black.

At this stage was when the bike struggled to start from cold and now only occasionally fires and runs really rough before cutting out and won’t start again.

Noticed that 2 of foam pods had holes in them and thought this might be a result of the back fires through carbs and bits might have ended up in carbs so stripped, blew all jets out and checked float heights. Repaired foam pods with some filter foam I had (will be changing to better smooth flow pods a bit later).

No change

Re-checked static timing – OK. Massive spark at all plugs but all plugs wet (when trying unsuccessfully start).

Can’t see plugs not sparking under compression suddenly?

Your thoughts and advice appreciated
Phil
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 #1 on: November 24, 2018, 12:57:50 AM »
Phil, try a new set of plugs, sounds like they might be failing under compression mate.

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #2 on: November 24, 2018, 10:49:12 AM »
That's my natural thought in the circumstances Bryan but thought why would all 4 fail at once! I have DR8ES and NGK Resister caps. Thinking whether double resister (plugs and caps would have any bearing on the running (or failure) when used with Boyer system?
Thinking of going for D8ES
Phil
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 Laverda Dave

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Re: CR750 Running (or not running!) issues
« Reply #3 on: November 24, 2018, 11:09:36 AM »
Phil, I understand you either have a resister cap or plug but never both? I would try the D8ES plugs as you mentioned and I think your problem will be cured.
Nice video and awesome looking (and sounding) replica.
Dave
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #4 on: November 24, 2018, 11:41:21 AM »
Phil, I understand you either have a resister cap or plug but never both? I would try the D8ES plugs as you mentioned and I think your problem will be cured.
Nice video and awesome looking (and sounding) replica.
Dave
Thanks Dave, just doing a bit of research and found on the .net site that some people have had trouble with the 8 plug in cold weather. Just thinking that this problem only occurred since the cold weather arrived, wondering whether a 7 rated plug Ward be better with this set up I have on the CR?
What do you think?

Sent from my Moto G (5) using Tapatalk

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 Trigger

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Re: CR750 Running (or not running!) issues
« Reply #5 on: November 24, 2018, 12:52:03 PM »
It depends on how wet the plugs are, could be a flooding problem from too much fuel  ;)
Between 7 & 8 there is not much difference but, always worth a try.   

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #6 on: November 24, 2018, 01:16:01 PM »
It depends on how wet the plugs are, could be a flooding problem from too much fuel  ;)
Between 7 & 8 there is not much difference but, always worth a try.
It's funny it's happened on all 4 cylinders at once though Graham - that's what's making me think about temperature range of plugs? ((With drop in temperature over period when problem has occurred)

Sent from my Moto G (5) using Tapatalk

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 JamesH

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CR750 Running (or not running!) issues
« Reply #7 on: November 24, 2018, 02:10:56 PM »
Def worth trying a D7ES plug. Also, where did you buy your plugs? I had issues recently with a set of D8ES plugs, bought from a reputable source. But, I suspect they were duff units..changed them, transformed the running of the bike...


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Offline hairygit

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Re: CR750 Running (or not running!) issues
« Reply #8 on: November 24, 2018, 02:17:21 PM »
The market seems flooded with fake plugs at the moment! There was a thread about it very recently.
If it's got tits or wheels, it's hassle, if it's got both, RUN!!!

Online K2-K6

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Re: CR750 Running (or not running!) issues
« Reply #9 on: November 24, 2018, 03:33:32 PM »
I was also thinking along the lines of Trigger, sounds like an excess of fuel. Does it smell petrolly?

If it's back firing then it's got sparks.

Boyer are very specific about resistance,  and you have got commonality of error across all four if you've got plugs and caps out of spec.

Offline Laverda Dave

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Re: CR750 Running (or not running!) issues
« Reply #10 on: November 24, 2018, 05:11:09 PM »
Hairy, I was chatting to the main man at the NGK stand at the bike show. I asked him how do we spot a fake, he said he couldn't tell me as this would get back to the fakers! Very odd, I thought they would do everything they can to publicise how to spot a fake? I mentioned about the logo rubbing off and the core not being made of copper, he appeared surprised. All he could say was to buy from a reputable seller.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Trigger

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Re: CR750 Running (or not running!) issues
« Reply #11 on: November 24, 2018, 06:06:04 PM »
Phil, I understand you either have a resister cap or plug but never both? I would try the D8ES plugs as you mentioned and I think your problem will be cured.
Nice video and awesome looking (and sounding) replica.
Dave
Thanks Dave, just doing a bit of research and found on the .net site that some people have had trouble with the 8 plug in cold weather. Just thinking that this problem only occurred since the cold weather arrived, wondering whether a 7 rated plug Ward be better with this set up I have on the CR?
What do you think?

Sent from my Moto G (5) using Tapatalk

Moist, damp, wet air doesn't flow through foam filters very well in the winter. This will drop the air to fuel mix  :o You could always leave it to the summer for better running  ;)

Offline philward

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Re: CR750 Running (or not running!) issues
« Reply #12 on: November 24, 2018, 07:05:31 PM »
Thanks guys (sorry been out all day) - too much fuel theory makes sense except haven't changed anything between good and bad running. Graham's cold damp air comments make sense, I think it's between that, fake plugs and plug temperature range (my set up might be sensitive to this) that makes sense to me. I'll try start up without foam filters, then swap plugs from my standard K2 (although R plugs) them order some none resister 7's from an NGK UK recommended stockist

Sent from my Moto G (5) using Tapatalk

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 #13 on: November 24, 2018, 09:07:17 PM »
Just ordered 4 x D7EA's from Europarts - £8.29 delivered! (discount code END35) - Got to be genuine from a company that size surely!
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 Moorey

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Re: CR750 Running (or not running!) issues
« Reply #14 on: November 24, 2018, 10:39:15 PM »
Have you done a compression test on it.

 

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