Topic: Engine losing power when accelerating

[Heyeveryone]

Hi everybody.

Need your opinion. I just took my '73 350f for her maiden voyage after being restored over the winter/spring.

I noticed that the bike seems to lose power when I rev the throttle hard. It sounds like it's getting bogged down. It also seems to lose power when going up a hill, and seems to "sputter" a bit. Random small bursts of acceleration.

At first I thought this was a clutch issue, but I do not think it is anymore. It feels more like either one cylinder is firing inconsistently, or a jetting issue, or both?

What are your thoughts? Just looking for some guidance before I start hunting down the problem.

[eislon]

Make any mods?  info on what was done mechanically on the restoration would be really helpful

[xenoscr]

General stuff:

• Check the plugs for spark: pull each plug, keep the kill switch off, and turn over the starter with the plug grounded to the bike somewhere. Do you see spark?
• While you got the plug out, how do they look, dry or wet? Wet could indicate too much gas, white to little.
• Did you sync the carbs with a vacuum gauge? Bench sync with a paper-clip/thin-wire is good but vacuum gauge is superior. Do they need synced?
• Pods or airbox? I had TONS of trouble getting the jetting right for pods and finally ditched them for the stock airbox. To keep my bike running in the mid-range with pods I had to jet so big I practically was spewing raw gas out my exhaust. That and I would stall out with a strong cross breeze.

Sputtering under load and while accellerating sounds like jetting to me, at least similar to the struggles I had in the beginning before I went though several dozen jet combinations. (i.e. school of hard knocks.) This is just some stuff I would check, like eislon posted, some details on your exact setup might help someone diagnose the issue more accurately than running through a big check list.

[HondaMan]

Try a test run with the gas cap loose on the tank. If the air vent is plugged, it will act just like this symptom, too. It is then not draining fuel into the carbs fast enough.

[xenoscr]

Try a test run with the gas cap loose on the tank. If the air vent is plugged, it will act just like this symptom, too. It is then not draining fuel into the carbs fast enough.

Oh, good one! I had forgotten about that. I sealed my tank while doing my restoration work... sealed the gas cap vent too. Woops! I think I was my own worst enemy back then. 

[Heyeveryone]

Thanks so much for the responses guys.

That gave me plenty of things to think about.

So, no engine modifications. Everything in the engine is totally stock. The only modification is that I switched from the stock air box to pods.

As far as the spark plugs go, they are not wet at all, and not white. Just light brown/tan (as I understand they should be)

All plugs appear to be getting spark, but I will double check.

I will try opening the gas cap this weekend. It does sort of sound like the bike might not be getting enough gas.


Thanks again everyone!!

[HondaMan]

The only modification is that I switched from the stock air box to pods.

Stop everything else and put the airbox back on. That's where the trouble is...pods DO NOT WORK on these bikse, and the smaller the engines, the worse they DO NOT WORK. Almost everyone here knows my 'stance' on these, and for good reason. Honda spent a LOT of engineering time and $$ to get the airbox situated to make it work on such small carbs, and pod filters completely destroy the carbs' ability to mix fuel. Someday I will write up the entire analysis of it and put it into the Thoughts of Hondaman section so those who care can learn about it.

[xenoscr]

The only modification is that I switched from the stock air box to pods.

Stop everything else and put the airbox back on. That's where the trouble is...pods DO NOT WORK on these bike, and the smaller the engines, the worse they DO NOT WORK. Almost everyone here knows my 'stance' on these, and for good reason. Honda spent a LOT of engineering time and $$ to get the airbox situated to make it work on such small carbs, and pod filters completely destroy the carbs' ability to mix fuel. Someday I will write up the entire analysis of it and put it into the Thoughts of Hondaman section so those who care can learn about it.

I have to agree. HondaMan knows best. (btw: HondaMan, your book was an AWESOME resource, I probably thanked you a long time ago in a thread far, far away already but, THANK YOU!)

I struggled with those stupid pods, I'm a firm believer in the airbox being best. I avoided one for a long time because I had to source one first. The previous owner had thrown out the original! Just say no to pods. 

[Don R]

 I had a 400f That had pods on it when I got it. Hondaman is 100% correct. It only ran decent on the choke and at certain rpm's.
  Same with a cb750 and a KZ1000. A well known bike drag racer tuned the KZ for me but said it would never run right on the street until I put a stock airbox on it. Broke my heart and wallet. Cost me to tune it for pods and then $300 for the stock airbox. It's awesome now. L0L. 

[rupaulpierce]

Check the bullet connectors to the coils


Sent from my iPhone using Tapatalk

[DaveBarbier]

With pods you could be running lean. Try to apply the choke a bit when you’re experiencing the lack of power. If that helps, increase the main jet one or two sizes and raise the needle one notch.

I had a 550 with pods and it ran great.

[MauiK3]

Should be a law against pods and other such “improvements”
Same goes for most aftermarket intakes on cars and pickups, all hogwash.

[Duke McDukiedook]

Not exactly hogwash when used properly.
Pods work great on racebikes that are properly tuned that go WOT 100% of the time.
Cold air intakes on Honda cars with fartcan mufflers can give a 10HP boost over the stock-canned EPA intake exhaust setup.

[DaveBarbier]

Should be a law against pods and other such “improvements”
Same goes for most aftermarket intakes on cars and pickups, all hogwash.

No there shouldn’t, haha

[seanbarney41]

Pods do nothing on racebikes except provide filter material when other engine and carburetor modifications prevent the use of the original airbox.  Guys, the airflow restriction is NOT the airbox, it is your intake port.

[HondaMan]

Not exactly hogwash when used properly.
Pods work great on racebikes that are properly tuned that go WOT 100% of the time.
Cold air intakes on Honda cars with fartcan mufflers can give a 10HP boost over the stock-canned EPA intake exhaust setup.

Note highlighted keyword above.
On CARS, sure, because there is one intake manifold and the vacuum remains. Not so on lawnmovers, go-karts, and SOHC4/Honda Twins.