Electronic ignition

[p@ul]

I have a 750/4 sohc f2 that is a pig to start and warm up. Before i start taking it apart as a Cafe Racer project i want it running properly and i'm thinking seriously about replacing the the points with Electronic Ignition. Does any one here have any experience of fitting and tuning one of these and how much better the engine runs once fitted ?

Cheers Paul.

[mick]

Hi Paul just my 2 penneth a well set up CB750 with points and condensers should start dead easily,

personally i prefer the points coz at least if something packs up you can usually rig something to get you home

were as electronic ignition can leave you stranded, just my opinion  cheers Mick.

[keithK2]

Hi Paul,
I agree with Mick, if the timing and carb balancing is done carfully it makes a massive amount of difference to cold starting, idling and pick-up at all throttle openings. Having run-in my 750 K2 i also rechecked valve clearances, adjusted cam chain and  reset points gap (dwell).
Hope this helps.

[UK Pete]

F2,s have to be set up spot on and even then they dont like the initial warm up , reason is honda set them up really lean , and compensated with a fuel injector to overcome the flat spot from idle, there is a cure but it takes a bit of messing about, i have read somewhere ( i think on the honda chopper site) that you can drill out the idle jets ever so slightly to richen up the slow runing circuit, or you can buy the different jets from sirius,
Electronic ignition is definitely better than points, so i would recommend that, but wont give you many advantages to well maintained points, also i would consider rebuilding the carbs paying very close attention to getting the pump and injectors fully working as this has a huge influence on slow running and warm up, there are many posts if you search the forums or google
Pete

[K2-K6]

I knew two owners of the F2 when it was new and can add to the good advice above in that the original setup of the choke was done to allow the tickover to be 3000rpm at full choke.

They always seemed to start fine but would be difficult to pull away on if you backed the choke in too early as you'd have to keep blipping the throttle to get the accelerator pump to richen the mixture (it only pumps as you rotate the throttle, not when the carbs are kept at a steady state).

One of the owners always fretted about the revs that Honda had set it to on a cold engine but they assured him it was absolutely correct, it never gave any problems.

I know full well the pros and cons of different igniton systems but my experience with these motors showed me that they just aren't that senstitive for starting if they are even close to being accurately setup.

This is the most consistently successful method I've seen for starting the 750F2;-
Before you do anything you need to open and close the throttles twice to pump some neat fuel into it, then open the choke fully and hit the starter. It should fire and settle at about 300rpm, then just leave it for about 1/2 mins and you normally will here it start to run a bit too rich, so at this point you can start pushing the choke in to get it running evenly.

When it's hotter, you can just pump the throttle once or twice to get it to fire straight away.

Don't blip the throttles when you shut it down a this leaves neat fuel in the motor which during extended period will dilute the engine oil.

[SteveD CB500K0]

If you want to look at the Dyna S system, go to www.z1enterprises.com

They're a good price and the exchange rate is good too.

Jeff Saunders (the proprietor) is a member on sohc4.net and is a very knowledable and helpful chap.

[Waggles]

For what its worth I am in the non electronic camp. As K2 says for starting etc a well maintained and set up points based ignition system is more than good enough. When I first got my F1 on the road I had a fault where 2 cylinders stopped firing ( turned out to be a loose wire connection ) but in my lunchtime investigations I went through everything but didn't have any feeler guages and set the points by eye. When I got home I found ( obviously ) everything was way out, timing and dwell angle but the bike started OK and was rideable.

There is no doubt that electronic systems are better and require less maintenance, so by all means get one for those reasons but I don't think you will see much benefit in starting, look to the carbs as has already been said.

[K2-K6]

To add a bit more, I think either std or electronic switching is fine on these motors and wouldn't mind using whichever but if you are chasing a particular problem then in my experience you can spend money converting and find no improvement so still be puzzled by it.

Undoubtedly if you run a weak mixture (classic F2 at low throttle) then having a really decent spark should always help to ignite the mixture reliably, but if the problem is caused by something then you'd probably have to get that sorted anyway.

As most people do with modern vehicles we all really use electronic systems now, but the only time I've had an engine stop for ignition was a car one on which the amplifier failed, it's not relevant to the F2 starting though, only as a longer term over view really.

[p@ul]

Thanks for the replies fella's... Some useful stuff to work on there. I was in the garage last night scratching my head at what to to first ( mechanically inept ) so i took the air box out, cleaned the plugs and inspected the points which all looked fine with out gapping them.  I started her up and while it took a short while to kick in, not half as bad as before, it seemed to hold a fast idle on choke a lot better. Am i right to suspect the idle/primary jets need looking at ?. It still misfired when i closed the choke though but i guess i didn't leave it long enough to get really warm before closing it i guess.

[Yoshi823]

I used to run Andrews coils, NGK D8EV plugs & Boyer-Bransden electroic ignition on my CB750F2 special & never had any problems in hot/cold/damp/wet weather conditions. The pilot jets were never messed with despite S&B conical individual filters, but the float heights were decreased by 0.5mm to make things slightly richer off idle. The needles were raised & main jets from a CB750K7, which were 117.5s, worked perfectly.

[K2-K6]

Sounds like youv'e got a small improvement.

As an overview of this particular era it's probably fair to say that this is the start of running bike engines leaner to make them less poluting (particularly in USA) so where as previous models displayed more tolerance to precise jetting, ther is less room for margin on this model.

That doesn't mean it should run with faults, Honda did a good job of it and with it correct it will run very well so it has no inbuilt faults and you should be able to have it working perfectly well.

When you say it missfires on tickover is that without using the throttle at all? as that would suggest the idle jets are the first place to look if nothing else is obvious.

If it misses as you start to open the throttle it could be related to the accelerator pump (this sprays additional fuel into the carbs ONLY AS YOU TURN the twist grip) this is to overcome the weak running of the normal setup. It's a transition stage to make it accelerate cleanly without stuttering and if not working correctly would show as a slow or missfire response if not delivering enough fuel during that increased damand.

There are quite a few on here that have worked on this area of the F2 so would be confident of you getting it sorted, it's just a case of working through it logically.

[p@ul]

Sounds like youv'e got a small improvement.

As an overview of this particular era it's probably fair to say that this is the start of running bike engines leaner to make them less poluting (particularly in USA) so where as previous models displayed more tolerance to precise jetting, ther is less room for margin on this model.

If it misses as you start to open the throttle it could be related to the accelerator pump (this sprays additional fuel into the carbs ONLY AS YOU TURN the twist grip) this is to overcome the weak running of the normal setup. It's a transition stage to make it accelerate cleanly without stuttering and if not working correctly would show as a slow or missfire response if not delivering enough fuel during that increased damand.

Exactly that... The misfire is as i twist the throttle and clears after about 3000 rpm when all rattles and misfires disappear and the motor sounds sweat.... BTW the bike is a US model !!

You may just be onto something here K2, thank you. I've just got to find where the hell this accelerator pump in located now 

[K2-K6]

Ah ha, could be getting somewhere......

The original set-up of this era acknolwledged that to lower emmisions you'd have to run the engine as lean as possible when now demand to pull the bike along was made. This ordinarily for any petrol engine is insufficient to get it to accelerate very easily at all......sooooo they specified an accelerator pump (fairly crude but easily effective) which sprays additional fuel straight into the carb venturi and bypasses all the other static jetting. This only happens as you are turning the twistgrip (this why I referred to giving a couple of twists before a cold start) The result being that the motor easily accelerates up into an area of carburation that is fully into running on the main jetting of the carbs then it would be away with no problems. All smoothness and light, but wthout this asistance it would be a bit of a pig.

UK Pete on here is one I've known to recently rebuild just this particular piece on his restored F2 so he may be the best to describe it for you. (he may have a bit on here already if you read his restore blog for the F2)

The USA model F2 and the one shipped here were all but identical so that's not a compromise as far as I know, The carburation strategy is common to both the F2 and the K7 which were sister bikes spec wise.

I hope you get it sorted out as they are really good to ride I think.

[p@ul]

Thanks fella...... I've started the strip down now so when i do pull the engine out i'll be able to inspect it more closely and maybe replace parts that are suspect. That is a long way off yet though. In the mean time at least i know it starts and runs 
Thank you all for your valued input.

There will be many more questions that pop up over time i'm sure, some will be silly due to my mechanical ineptitude 

[p@ul]

If you want to look at the Dyna S system, go to www.z1enterprises.com

They're a good price and the exchange rate is good too.

Jeff Saunders (the proprietor) is a member on sohc4.net and is a very knowledable and helpful chap.

Hi Steve, that set up.might just be worth a punt but I just need to check the state of the accelerator pump before i proceed.... Thanks for the advise.