SOHC.co.uk Forums > CB350/400
CB400/4 ENGINE STRIP, ASSESSMENT AND REBUILD BY JULIE - NOW COMPLETE
Nurse Julie:
--- Quote from: rozabikes on December 01, 2017, 11:32:24 PM ---
--- Quote from: Nurse Julie on December 01, 2017, 08:27:36 PM ---
--- Quote from: 3scs on December 01, 2017, 08:18:03 PM ---That looks good if it’s not top secret what has been done to get to that condition
--- End quote ---
No secret. Hot wash to remove all grease etc. Acid dipped to remove all old paint / oil. Another hot wash. Soda blast and hand finish to remove any old corrosion that may be left in the nooks and crannies. Painted with engine enamel, air cured for 24 hours then final cure in the oven. The good outcome is definitely due to the prep.
--- End quote ---
Julie, was final painting farmed out or DIY?
--- End quote ---
Trigger did it and he has many engines on the paint list at the moment but, I did squeeze mine in.
Rozabikes Tim:
--- Quote from: Nurse Julie on December 01, 2017, 11:38:59 PM ---
--- Quote from: rozabikes on December 01, 2017, 11:32:24 PM ---
--- Quote from: Nurse Julie on December 01, 2017, 08:27:36 PM ---
--- Quote from: 3scs on December 01, 2017, 08:18:03 PM ---That looks good if it’s not top secret what has been done to get to that condition
--- End quote ---
No secret. Hot wash to remove all grease etc. Acid dipped to remove all old paint / oil. Another hot wash. Soda blast and hand finish to remove any old corrosion that may be left in the nooks and crannies. Painted with engine enamel, air cured for 24 hours then final cure in the oven. The good outcome is definitely due to the prep.
--- End quote ---
Julie, was final painting farmed out or DIY?
--- End quote ---
Trigger and he has many engines on the paint list at the moment but, I did squeeze mine in.
--- End quote ---
Mmm favouritism then.... Rattle can job or proper set up?
Nurse Julie:
--- Quote from: rozabikes on December 02, 2017, 07:53:16 AM ---
--- Quote from: Nurse Julie on December 01, 2017, 11:38:59 PM ---
--- Quote from: rozabikes on December 01, 2017, 11:32:24 PM ---
--- Quote from: Nurse Julie on December 01, 2017, 08:27:36 PM ---
--- Quote from: 3scs on December 01, 2017, 08:18:03 PM ---That looks good if it’s not top secret what has been done to get to that condition
--- End quote ---
No secret. Hot wash to remove all grease etc. Acid dipped to remove all old paint / oil. Another hot wash. Soda blast and hand finish to remove any old corrosion that may be left in the nooks and crannies. Painted with engine enamel, air cured for 24 hours then final cure in the oven. The good outcome is definitely due to the prep.
--- End quote ---
Julie, was final painting farmed out or DIY?
--- End quote ---
Trigger and he has many engines on the paint list at the moment but, I did squeeze mine in.
--- End quote ---
Mmm favouritism then.... Rattle can job or proper set up?
--- End quote ---
Favouritism, ha, your having a laugh Tim. Customers come first and as I'm told regularly, I'm not a customer ::) Rattle can enamel. Trig heats the cases and the paint before applying, it gives a much better adherence and finish.
K2-K6:
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400 Four detonation
« on: Today at 09:05:04 AM »
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Alright, I know I " go on about it" but been looking at why I feel detonation can easily occur on this engine given the right / wrong conditions.
As others pointed out you normally associate lean mixture with something like this, which is not obviously the case if jetted properly, you'd have thought?
A characteristic of slide carbs is that you can create it with how you ride, even if setup is correct.
Above should be a dyno trace that Jensen has kindly shared of his 400 Four running in 4th gear with throttle rolled open in that one gear to build the power curve you see in top traces.
The really interesting bit is the lower trace, left scale is mixture with rpm along the bottom. It's obvious from that peak leading up to 4000rpm that it's running toward an over lean condition. Complete burn is considered to be 14.7 parts air to 1 part fuel. Most engines won't get that close. During acceleration you'd expect closer to 12 to 1 to make it move, with cruising state in between the two.
It's not a wrong setting on here, just characteristic of running from low rpm to high in one gear which is needed for the dyno plot.
What it does is the vacuum the engine draws at low rpm with throttle wide open cannot match the flow the carb venturi is making, resulting in loss of vac on the main jet, and so less fuel than ideal is pulled from float chambers ( it's this bit that PD carbs fill in with accelerator pump, clever a?) you can't jet your way out of it as the carb and main jet is almost fully open. It's really a failure of slide carbs used in this way and what would be termed "lugging " the motor in high gear.
In addition, the ignition advance reaches max around 3000rpm and quite early for full load application ( more suited to cruising on light throttle to give good economy) so in that lean peak area you've also got probably too much advance for a short period.
Put those conditions together, perhaps riding along into a headwind, fith or sixth gear, trying to keep up speed at lowered rpm and you've got classic detonation. Riders with experience would recognise it's not pulling properly, but if the circumstances are held like that without the engine accelerating through that, it will most likely detonate. It'll only take a few minutes like that to start the destruction of the pistons and rings.
You can't jet it differently, it's just how you ride it. They need to be revved if you want them to go.
You've either got to back down the throttle or drop gears and spin it to higher revs.
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K2-K6:
The above post is copied from another thread that I've started with a relevant heading to make it easy to find in future.
http://www.sohc.co.uk/index.php/topic,14609.msg118849/topicseen.html#new
Thought I'd better explain as Julie requested that I post it over here otherwise it may look a bit like random ranting by me. ;D
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