Friday, November 21, 2014

Honda GL1000 Single Carb Conversion?

We've been at our Winter retreat for 10 days already. Been working on minor up the yard and some RV repairs which have stacked up over the past 9 months.
Finally took a little time and removed the Gold Wing carburetors. Prior to removing them I performed a compression test on the engine....PSI ranged from 139 psi to 142 psi across the 4 cylinders....sign of a perfectly healthy engine.
 The OEM carbs have caused me minor problems for the past 3 years and have never worked as they should. If the bike sat for more than 2 weeks it would flood and not want to run, usually flooding and gas would expell through the exhaust manifold. After a thorough warm up the bike would then run, but never as good as I thought it should. I got into the habit of starting the bike once each week and warming it up to riding temperature, even if I wasn't riding it. This weekly procedure at least kept the bike ready to ride. But last August it basically "died" on me, not getting fuel to the right cylinders at lower RPMS....engine would run at 4000 RPM's and higher but not in the lower ranges.

 I have a few different options:
1) Rebuild them myself.....this option would be the best. A rebuild kit from "Randakk" runs about $189.00. But the 4 top plastic "plugs" in the top covers have rotted and one had a hole in it last Winter which I jury rigged a fix. I cannot find any replacement parts for these so I'd need to buy a set of 4 donor carbs to replace the top of each CV chamber.  Also I don't have the equipment to properly "soak" them to clean them out. I simply did not want to tear into the complex "4 carb" rack. Once mounted on the bike the multiple adjustment screws are nearly impossible to access. I attempted to remove the bowl drain plugs last way to get the soft brass plug screws loose without stripping them. The OEM design is definitely the best, but overly complex and difficult to keep working properly.
2) I had a quote for a rebuild from a retired Honda mechanic....quote was for $850.00 to rebuild / tune the bike. Way more than I am willing to spend. A local shop would rebuild them if I brought them in...cost of rebuild kit plus 3 - 4 hours labor. Likely a total of $500.00 - $600.00 by the time it was done.
3) Go to a more simple alternate carburetion. After many hours of research I found multiple different bolt on options:
        This set up utilizing a "Solex" type one barrel carb sells for around $400.00. I don't like to looks of the squared plenum, I would think that fuel mixture flow would be disrupted.
 This bolt up set up about the same...same carb and slightly better manifold.....$400.00.

This design appeared to be the best...again with the VW one barrel carb and a better designed intake....$580.00

After more research I just don't think the Solex one barrel carb would be sufficient to handle all ranges for the Gold Wing. Read a lot on the subject.... many have installed and like the above set ups.

I finally decided to go a different route and ordered the items below today. This will require some design of my own and won't be a "bolt on and go" scenario, but talking with folks who have built / used them, I think it will be an easier option rather than  maintaining the more complex OEM system. Also should be a better fit for the ranges needed for highway / street riding than the Solex single barrel carb. I found some information from a guy on the Internet who has done this exact conversion. Trying to follow his "lead" as close as I can. He put a lot of effort into research / developement while designing his conversion. 

                VW Type 4 Bus engine Plenum.......

            Weber "32DFT" 2 barrel carb using a progressive (linkage operated) secondary.

My experience with the Weber carbs has been excellent over the years. I once replaced a troublesome Solex 2 barrel with a Weber 2 barrel on a German car I had years back. The Weber was much better and trouble free.
I will need to come up with either piping or tubing to connect the plenum to the heads. The stock intakes which attach to the heads will be retained and used. I've also purchased a "universal" throttle linkage kit which will allow used of the OEM throttle cable. This project will require a bit more labor to install but I think the final installation will be much easier to maintain and tune than the OEM setup once everything is dialed in. Hopefully I won't regret this decision....Discussing the above set up with folks who have toyed with the single carb conversion, I found that the chosen setup should be the best alternate to the OEM system...we'll see.....

Slowly acquiring required parts. The manifold / linkage / air cleaner assemblies arrived. The Weber carb was finally shipped earlier this week. Ended up that the carb vendor was on vacation for a couple weeks so shipping was delayed until this week.
Went out yesterday and found some fuel "friendly"  1 1/2" intake hose. Decided to attached directly to the intake manifolds with the fuel hose. That required removing the rubber intake attachments on the OEM manifolds. I did not realize the rubber was perminantly bonded to the intake alloy manifold. I damaged the first one to remove it. The "lip" on the OEM manifold (which the new fuel runner attaches to)  is quite small. Hopefully I can acheive a positive seal with clamps. I'll go ahead and strip the rubber off of the three remaining manifolds today. Others use a rigid pipe (of different types) and retain the OEM manifold / rubber. If my technique fails, I went ahead and ordered a replacement set of used OEM manifolds ($18.00 for 4 with free shipping.)
I found another design where as folks are making single carb manifolds out of sch. 40 PVC pipe with reported success. They use single barrell VW carbs though, which I decided to avoid.
Slowly but surely I'm gaining some progress. If all goes well I should have everything assembled in the next few days. The throttle linkage would be the next challenge, but I have a couple different options in mind.
The carb comes with an electrically activated choke assembly. A number of set ups I've seen remove the electric choke activation module due to clearance issues...some running without a choke control. I'll figure that out as I go.....We'll see how the bike starts without a choke and go from there. The Weber carb uses an accelerator pump so fuel enrichment can be acheived by a twist of the throttle.
One problem I've read about is a "Hydro-lock" situation, where the cylinders flood with fuel, locking the engine. Every instance of this scenario has been due to someone leaving the fuel tank petcocks open and fuel leaking past the needle valve, effectively flooding the engine. I habitually close petcocks when engines shut down so this should not be an issue for me.
Total investment in the assembly is currently @ $300.00.


Richard M said...

Looking forward to hearing about this one. When I first saw the title, my first thought was a two barrel Weber would be about right for the 1 litre engine. Why are folks using Solex carbs? I would think that the Weber would be more "tuneable". Plus you completely eliminate the need to balance the carbs. At one of the BMW rallys there was an R100 with a t barrel Weber and it was about the smoothest airhead you ever heard.

Good luck on the conversion!

BMW HACKER said...

I think the Solex conversion is they work with the larger 1600 cc VW engines. The 2 bbl. Weber should offer better performance though...anyway I hope so.
Watched a number of videos of Gold Wings running the Solex 1 bbl. They sounded a bit "anemic" to me under acceleration.

Steve Scott said...

Fwiw, conversing with those that have toyed with the idea may prove distastefully advantageous in the end.
A thorough understanding and applied effort in construction is required of that intake manifold if superior results are to be expected.
Done correctly, that carburetor requires no recalibration on a stock engine.
...just a heads-up...

Gila Mtns.

Gila Mtns.