Won't return to idle/slight oil seep...

[Bryanj]

They were for the Yanks to stop people "fiddling" in those states with emmisions rules

[McCabe-Thiele (Ted)]

One advantage of the black stoppers is that they give you a visual reference point - i find it easy to loose track of how many turns the screw has moved especially if you have been tinkering with the settings over a few days.

[Trigger]

Black airscrew limiters, I'd view them as obviously limiting movement, but think they look to do tbat specifically in relation to situations that we probably don't encounter in these lowlands 

For screws set at sea level, then riding up to high altitude, they seem to give a set adjustment to compensate without having to do the "turns counted out" thing. In other words you could easily set them at one end or t'other in that scenario. And maybe an early nod to restriction on adjustment for emissions legislation in some market.

Outside that, they dont seem to do much, but some may want them for originality purposes.

I have never understood this sea lever and high altitude 

I have rode old Honda's though out the world, starting at sea level, up to 2500 meters and back down to sea level over and over again. On all these trips i have never tinkered with the carbs and the bike has always run spot on.

[McCabe-Thiele (Ted)]

I believe it is due to the density of the atmosphere being rarer at height that leads to engines effectively running rich due to lack of oxygen - iirc it is at extremes of altitude and worse in highly tuned engines. Might be that as bikes rely on gravity rather than fuel pumps the effect is mitigated.

[Trigger]

My experience I never had problem driving highly tuned engine cars with fuel pumps from the UK, crossing the Austrian alps, the full length of Yugoslavian mountains and crossing the northern Greek mountains. Diving a Noble M12 or a UVA sandrail that had twin choke Webber's      

[taysidedragon]

My experience I never had problem driving highly tuned engine cars with fuel pumps from the UK, crossing the Austrian alps, the full length of Yugoslavian mountains and crossing the northern Greek mountains. Diving a Noble M12 or a UVA sandrail that had twin choke Webber's      

I think you need to get to much higher altitudes before you'll notice any loss of performance. The highest roads in the Himalayas,  for example. For most of us we'll never need to worry about it.

[McCabe-Thiele (Ted)]

On a related topic all my bikes & cars drove much better after a decent downpour of rain  - probably explains a brief period when ICE manufacturers toyed with water injection.

[Mikep328]

The not-returning-to-idle seems to have been caused by the high-idle stop being out of adjustment!  The manual calls for .012"/.3mm clearance and there was none. It was holding the throttle slightly open which got worse as the engine heated up.  I adjusted the clearance per the Honda specs and, once the engine was good and warm - which takes more time than I would have thought - I adjusted the idle stop screw to 1200 RPM.  From that point on the engine returned to that RPM when the twist grip was returned to the idle position.  But the idle is a bit rough and the engine still bogs when opening the throttle quickly. 

further re the bog - I haven't found any info in the Honda service manual or a Clymers that mentions changing the position of the needle to adjust the mixture in the range the needle controls.  I'm NOT saying there isn't any info, just that I haven't found it.  I'd think that raising the needle might reduce/eliminate the bog.   Any thoughts/experience re this?

I'm definitely going to pull the carbs/check/adjust everything out but we're going out of town on Tuesday for a week so that will wait until we return. 

[Deek]

I've felt the loss of power in a modest vehicle at 9500 feet altitude in Colorado.  There are suggestions of losing 3% of power per 1000 feet of altitude gain, also that engines can run on lower octane fuel in higher altitudes than elsewhere. In certain parts of Colorado fuel stations have sold petrol with octane levels as low as 85.

I guess the impact of altude is felt more on lowly poweredengines. Presumably manufacturers set engines up to run optimally at some average altitude above sea level. No idea whether it varies by manufacturer or intended market. Tibet might be require  some adjustments with the lowest city over 9000 feet and an average altitude over 14000 feet. Probably not many 400 fours there though.

[K2-K6]

The not-returning-to-idle seems to have been caused by the high-idle stop being out of adjustment!  The manual calls for .012"/.3mm clearance and there was none. It was holding the throttle slightly open which got worse as the engine heated up.  I adjusted the clearance per the Honda specs and, once the engine was good and warm - which takes more time than I would have thought - I adjusted the idle stop screw to 1200 RPM.  From that point on the engine returned to that RPM when the twist grip was returned to the idle position.  But the idle is a bit rough and the engine still bogs when opening the throttle quickly. 

further re the bog - I haven't found any info in the Honda service manual or a Clymers that mentions changing the position of the needle to adjust the mixture in the range the needle controls.  I'm NOT saying there isn't any info, just that I haven't found it.  I'd think that raising the needle might reduce/eliminate the bog.   Any thoughts/experience re this?

I'm definitely going to pull the carbs/check/adjust everything out but we're going out of town on Tuesday for a week so that will wait until we return.

Good progress with sorting out basic throttle rest position to get at least a consistency there.

This really is tied up in idle circuut competency, they lead the mixture in with a gradient to fully "knit" together with the main jet and needle flow in getting a seamless transition.  Without at least verifying the carbs and their adjustment it's hard to get decent view of what is happening.

With those engine, wide open throttle with high gear and low speed is not where you want to operate, but given the correct gear ratio, then wacking the throttle open shouldn't give that bog, it should just run up the revs without complaint.

The scenario that gives the "bog"  is insufficient fllow/metering of idle circuit to get the fires going, then to bring the response fully onto main jet. If this doesn't happen and it's gone too lean from idle giving insufficient mixture, then further opening the throttle slides just exacerbates this by then dropping vacuum to also not pull fuel through main jet route. One needs the other to lead it. Usually you need to close the throttle a little to help increase the vacuum under the slide, then it'll start to pull up through the flat spot but you'll normally have to baby it to get through there.

Focus on impeccable idle circuits, then the rest Usually falls into place on these.

Also, idle curcuit are absolutely key to getting smooth idle rpm and quiet running. One out of kilter can make it sound like a bag-o-nails.

[Skoti]

Another scenario that gives the 'bog' is aftermarket needles.
Many cheapo needles have incorrect taper profiles compared to the genuine Honda items.

The transition from idle jet to main jet is affected exactly the way you describe.


This topic has in the past been discussed over on the USA SOHC site.



Good luck

Skoti

[Skoti]

Black airscrew limiters, I'd view them as obviously limiting movement, but think they look to do tbat specifically in relation to situations that we probably don't encounter in these lowlands 

For screws set at sea level, then riding up to high altitude, they seem to give a set adjustment to compensate without having to do the "turns counted out" thing. In other words you could easily set them at one end or t'other in that scenario. And maybe an early nod to restriction on adjustment for emissions legislation in some market.

Outside that, they dont seem to do much, but some may want them for originality purposes.

I have never understood this sea lever and high altitude 

I have rode old Honda's though out the world, starting at sea level, up to 2500 meters and back down to sea level over and over again. On all these trips i have never tinkered with the carbs and the bike has always run spot on.

To be honest I do notice a slight power loss when crossing the higher alpine passes in Austria and Switzerland on my CB750F1 and my Norton Commando. (But I've never tinkered with the carbs)

It's not noticeable on my BMW R1150RT, but it has fuel injection and an engine management system so I suppose that compensates the air/fuel ratio accordingly? 

[Mikep328]

The slight oil seep I have does not appear to be from the pan gasket. It is dripping from the cover on the left side of the engine adjacent to the pan and then down the side of the pan.  So based on an earlier post, the suspect is the gear change seal?

I suppose I could use the oil seep to determine if there is oil in the bike as per old BrittBikes - "If it's not leaking it's out of oil!"  But I'd prefer the typical Honda method - no oil leaks at all!

[Orcade-Ian]

Mike,
My normally very oil tight 350/4 developed a drip from the sump a few months back, so I removed the L/H side cover and there was quite a misting of oil around the sprocket/gearchange shaft/oil pump.  I cleaned the area with brake cleaner and ran the engine for a while.  My leak was from the 'crimp' on the oil light switch where the case is rolled over the insulator.  Replaced the switch and it's now back to Honda oil tightness.  Might be worth a look.  It's 20 years since I restored the 350/4, so I can't grumble really and I had a spare switch from my 400/4.
Ian

[Nurse Julie]

A good diagnostic is to remove the side cover, clean up the area thoroughly, puff with talcum powder, run engine and you will see a witness mark of oil coming from whichever seal / O ring is leaking.