Topic: '78 Hondamatic starting problems

[Honda4]

I have triked my '78 cb750A Hondamatic. In so doing I had to remove the stock mufflers and replaced them with can opener style inserts of about 6". I have removed the stock air box & replaced it with individual foam pods. The stock carbs have been re-jetted to 120's. It runs great. My problem is that it won't start when cold even with the full application of the choke. I must put my hand over 1 or 2 carbs before it will catch and start. Once it is warmed up it will start with no problem. Any help that can be offered is appreciated. I will answer as many questions as i can on this build. Thanks

[Honda4]

It's surprising what a little sleep and a fresh perspective can do. I readjusted the choke cable and finally got the choke to fully close. It now starts like new.

[Honda4]

Now on to the next set of problems (?). Since I have replaced the stock air box with individual foam pod filters but retained the original PD carb bank there is no method of obtaining vacuum to operate the accelerator bump up mechanism. My thought is to rig up a port on one of the carbs and attach the vacuum hose there but, wondering if one carb can generate a strong enough vacuum signal near idle to operate this system? Or, perhaps it's not needed or is it just best to change out for a set of K series carbs. Also, does anyone have any tips on a method or tool I can use so as not to incinerate  my hand when adjusting these carbs. They are set in one heck of an awkward position. Thanks, any input on these issues would be appreciated.

[jukku]

The accelerator pump is mecanical, not vacum acctuated!

[05c50]

The vacuum source for the solenoid is from a nipple on one of the carbs (number two I think), the hose from the solenoid to the air box is a vent. Using pods shouldn't affect the vacuum for the solenoid. Look at this illustration: https://www.cmsnl.com/honda-cb750a-750-hondamatic-1978-usa_model7237/partslist/E++21.html#results

.....Paul

 

[Honda4]

Thanks for the input folks. I've printed the carburetor solenoid schematic and will trouble shoot it to be sure it's working although, with a bit of an increase in idle rpm it did not stall and/or lurch too badly. I've also adjusted the accelerator pump and will recheck same for proper operation.

I took  the trike on it's first real test ride yesterday of about 20 miles. Even with the 120 jets I believe it's running very lean. It had a hard time maintaining speed with small amounts of throttle input but with approx. 50% opening it would take off and keep accelerating. I'll pull the plugs today and see how they read.

Does anyone have a suggestion for alternative jet size? Also, has anyone had experience utilizing K carbs on "A" engines?

Thanks again for all the help.

[Honda4]

Being new to the Club, I'm not sure if this is how to proceed but, I thought I'd keep a chronicle of how things are moving on this project should others run into similar issues.

Today I pulled the plugs and they confirmed the engine is running very lean. I replaced the 120 jets with 128's. I checked the accelerator pump & accelerator bump up solenoid to insure they were both working. I adjusted the bump up, fired it up, adjusted the jets for max rpm & headed out on a test ride. It ran much better but still felt lean with minor balking problems at low rpm. I pulled the plugs again and the indication was it was in fact, still running lean. When I get back to the shop I'm going to install 132 jets & test.

Other than that, I find that even after lubing the throttle cables and carb shaft twisting the throttle is very difficult. I'll try and fix that by stretching the return spring a bit. Any questions? please let me know. Thanks

[05c50]

I'm thinking that unless you're testing under WOT (wide open throttle), you probably don't want to go with larger main jets. Your slow jets and needle profile control most of the fuel metering during most driving modes.

....Paul 

[Honda4]

Thanks for your input. Would you make a recommendations as to needle position or change and slow jet size? I put the project together for my wife so that she would could get the experience of riding by herself. She will most probably use it around town and on local rides. I don't expect she will ever use much throttle. I look forward to hearing from you. Thanks again, Frisco

[05c50]

My Hondamatic is all stock, jets, exhaust, air filter and air box and I'm running stock jetting.  It sounds like you want good driveability as opposed to tire smoking acceleration. I would suggest that you increase the slow jets slightly and leave the needles alone. Besides, you're not going to get that kind of performance from a stock Hondamatic.

.......Paul

[Honda4]

Thanks for your response. I agree, I'm looking for good drivability & not super acceleration. The problem at this point is-it's still running too lean & needs more fuel. If that can be achieved via increasing the size of the slow jet, great. Can you make a recommendation as to slow jet size? As you know, the stock slow jets are very small. I use an #80 drill bit to clean them. Thanks again, Frisco

[05c50]

I'm kinda surprised that it's running so lean, are you certain that the float is set correctly?

.....Paul

[Honda4]

As you know the Hondamatic was not a tire smoker from the get go with 20 less hp. than the 4 speed (same) model. As for the floats, yes the level was checked via the manual and all OK. Thanks for mentioning that.

I agree with you, stock is fine but in this case there were a few more things to consider. A. In  building a trike, I was adding weight; robust swing arm, DNA rear axle, automotive tires and rims, fenders & braking system requiring I find as much power as possible without increasing engine displacement although, that's still an option. B. The stock mufflers would not fit with the new swing arm configuration so they had to be changed out for the aforementioned 6" can opener insert. D. Stock air box was removed in search of, again, more power. All those changes leaves me with a cool trike my wife likes but, running way too lean and not developing all the power is should for this configuration. All this, leads me back to the same spot, I need to fatten up the air fuel ratio. If you are aware of a method of doing so via an increase in the size of the slow jet, can you (or anyone else) make a recommendation as to size? Another avenue is to install K carbs. I have a few sets of those from other projects and wonder if you have had any experience making that swap?

Thanks again for your help,
Frisco

[jukku]

Hello. I used the stock airbox in all my Matics.

[Honda4]

Thanks for your response and input. I like what you've done with your bikes. One question please, did you need to change the main jets on the trike with the 4 into 1 exhaust? If so, can you provide the size?
Thanks,
Frisco

ps-- I like the use of the Vetter top box. I used the same one on my wife's trike.

[Honda4]

Also, where did you purchase the fenders for the trike? Thanks

[Honda4]

WELL, I'VE GONE FORWARD AND INSTALLED 1.32 JETS IN THE HONDAMATIC AND TOOK IT FOR A TEST RIDE. IT RAN GREAT; NO LONGER STUMBLED, PULLED HARD WITH ONLY A MINOR SURGING AT SMALL TO MEDIUM THROTTLE OPENING. JUST RIGHT FOR AROUND TOWN AND TRIPS. MY LAST CHORE IS TO FIND APPROPRIATE FENDERS AND SHE'S FINISHED. THANKS ALL FOR YOUR INPUT AND ADVICE.
FRISCO